Major storage layer refactoring to set the stage for clean GCM.

1) We now try to hand out cursors at a minimum.  There has always been
   a fairly clean insertion layer that handles encrypting message bodies,
   but the process of decrypting message bodies has always been less than
   ideal.  Here we introduce a "Reader" interface that will decrypt message
   bodies when appropriate and return objects that encapsulate record state.

   No more MessageDisplayHelper.  The MmsSmsDatabase interface is also more
   sane.

2) We finally rid ourselves of the technical debt associated with TextSecure's
   initial usage of the default SMS DB.  In that world, we weren't able to use
   anything other than the default "Inbox, Outbox, Sent" types to describe a
   message, and had to overload the message content itself with a set of
   local "prefixes" to describe what it was (encrypted, asymetric encrypted,
   remote encrypted, a key exchange, procssed key exchange), and so on.

   This includes a major schema update that transforms the "type" field into
   a bitmask that describes everything that used to be encoded in a prefix,
   and prefixes have been completely eliminated from the system.

   No more Prefix.java

3) Refactoring of the MultipartMessageHandler code.  It's less of a mess, and
   hopefully more clear as to what's going on.

The next step is to remove what we can from SmsTransportDetails and genericize
that interface for a GCM equivalent.

src/org/thoughtcrime/securesms/DatabaseUpgradeActivity.java

@@ -0,0 +1,148 @@
+package org.thoughtcrime.securesms;
+
+import android.app.Activity;
+import android.content.Context;
+import android.content.Intent;
+import android.content.SharedPreferences;
+import android.content.pm.PackageManager;
+import android.os.AsyncTask;
+import android.os.Bundle;
+import android.preference.PreferenceManager;
+import android.util.Log;
+import android.view.View;
+import android.widget.ProgressBar;
+
+import org.thoughtcrime.securesms.crypto.MasterSecret;
+import org.thoughtcrime.securesms.database.DatabaseFactory;
+
+import java.util.SortedSet;
+import java.util.TreeSet;
+
+public class DatabaseUpgradeActivity extends Activity {
+
+  public static final int NO_MORE_KEY_EXCHANGE_PREFIX_VERSION = 46;
+
+  private static final String LAST_VERSION_CODE = "last_version_code";
+
+  private static final SortedSet<Integer> UPGRADE_VERSIONS = new TreeSet<Integer>() {{
+    add(NO_MORE_KEY_EXCHANGE_PREFIX_VERSION);
+  }};
+
+  private MasterSecret masterSecret;
+
+  @Override
+  public void onCreate(Bundle bundle) {
+    super.onCreate(bundle);
+    this.masterSecret = (MasterSecret)getIntent().getParcelableExtra("master_secret");
+
+    if (needsDatabaseUpgrade()) {
+      Log.w("DatabaseUpgradeActivity", "Upgrading...");
+      setContentView(R.layout.database_upgrade_activity);
+
+      ProgressBar indeterminateProgress = (ProgressBar)findViewById(R.id.indeterminate_progress);
+      ProgressBar determinateProgress   = (ProgressBar)findViewById(R.id.determinate_progress);
+
+      new DatabaseUpgradeTask(indeterminateProgress, determinateProgress).execute(getLastSeenVersion());
+    } else {
+      updateLastSeenVersion();
+      startActivity((Intent)getIntent().getParcelableExtra("next_intent"));
+      finish();
+    }
+  }
+
+  private boolean needsDatabaseUpgrade() {
+    try {
+      int currentVersionCode = getPackageManager().getPackageInfo(getPackageName(), 0).versionCode;
+      int lastSeenVersion    = getLastSeenVersion();
+
+      Log.w("DatabaseUpgradeActivity", "LastSeenVersion: " + lastSeenVersion);
+
+      if (lastSeenVersion >= currentVersionCode)
+        return false;
+
+      for (int version : UPGRADE_VERSIONS) {
+        Log.w("DatabaseUpgradeActivity", "Comparing: " + version);
+        if (lastSeenVersion < version)
+          return true;
+      }
+
+      return false;
+    } catch (PackageManager.NameNotFoundException e) {
+      throw new AssertionError(e);
+    }
+  }
+
+  private int getLastSeenVersion() {
+    SharedPreferences preferences = PreferenceManager.getDefaultSharedPreferences(this);
+    return preferences.getInt(LAST_VERSION_CODE, 0);
+  }
+
+  private void updateLastSeenVersion() {
+    try {
+      SharedPreferences preferences = PreferenceManager.getDefaultSharedPreferences(this);
+      int currentVersionCode        = getPackageManager().getPackageInfo(getPackageName(), 0).versionCode;
+      preferences.edit().putInt(LAST_VERSION_CODE, currentVersionCode).commit();
+    } catch (PackageManager.NameNotFoundException e) {
+      throw new AssertionError(e);
+    }
+  }
+
+  public static boolean isUpdate(Context context) {
+    try {
+      SharedPreferences preferences = PreferenceManager.getDefaultSharedPreferences(context);
+      int currentVersionCode        = context.getPackageManager().getPackageInfo(context.getPackageName(), 0).versionCode;
+      int previousVersionCode       = preferences.getInt(LAST_VERSION_CODE, 0);
+
+      return previousVersionCode < currentVersionCode;
+    } catch (PackageManager.NameNotFoundException e) {
+      throw new AssertionError(e);
+    }
+  }
+
+  public interface DatabaseUpgradeListener {
+    public void setProgress(int progress, int total);
+  }
+
+  private class DatabaseUpgradeTask extends AsyncTask<Integer, Double, Void>
+      implements DatabaseUpgradeListener
+  {
+
+    private final ProgressBar indeterminateProgress;
+    private final ProgressBar determinateProgress;
+
+    public DatabaseUpgradeTask(ProgressBar indeterminateProgress, ProgressBar determinateProgress) {
+      this.indeterminateProgress = indeterminateProgress;
+      this.determinateProgress   = determinateProgress;
+    }
+
+    @Override
+    protected Void doInBackground(Integer... params) {
+      Log.w("DatabaseUpgradeActivity", "Running background upgrade..");
+      DatabaseFactory.getInstance(DatabaseUpgradeActivity.this)
+                     .onApplicationLevelUpgrade(masterSecret, params[0], this);
+      return null;
+    }
+
+    @Override
+    protected void onProgressUpdate(Double... update) {
+      indeterminateProgress.setVisibility(View.GONE);
+      determinateProgress.setVisibility(View.VISIBLE);
+
+      double scaler = update[0];
+      determinateProgress.setProgress((int)Math.floor(determinateProgress.getMax() * scaler));
+    }
+
+    @Override
+    protected void onPostExecute(Void result) {
+      updateLastSeenVersion();
+      startActivity((Intent)getIntent().getParcelableExtra("next_intent"));
+      finish();
+    }
+
+    @Override
+    public void setProgress(int progress, int total) {
+      publishProgress(((double)progress / (double)total));
+    }
+  }
+
+}