enable media forwarding

fixes #1362
closes #4589
// FREEBIE

src/org/thoughtcrime/securesms/mms/AttachmentManager.java

@@ -27,6 +27,7 @@ import android.provider.ContactsContract;
 import android.provider.MediaStore;
 import android.support.annotation.NonNull;
 import android.support.annotation.Nullable;
+import android.text.TextUtils;
 import android.util.Log;
 import android.view.View;
 import android.widget.Toast;
@@ -46,6 +47,8 @@ import org.whispersystems.libaxolotl.util.guava.Optional;
 import java.io.IOException;
 import java.util.concurrent.ExecutionException;
 
+import ws.com.google.android.mms.ContentType;
+
 public class AttachmentManager {
 
   private final static String TAG = AttachmentManager.class.getSimpleName();
@@ -279,5 +282,14 @@ public class AttachmentManager {
       default:    throw  new AssertionError("unrecognized enum");
       }
     }
+
+    public static @Nullable MediaType from(final @Nullable String mimeType) {
+      if (TextUtils.isEmpty(mimeType))       return null;
+      if (MediaUtil.isGif(mimeType))         return GIF;
+      if (ContentType.isImageType(mimeType)) return IMAGE;
+      if (ContentType.isAudioType(mimeType)) return AUDIO;
+      if (ContentType.isVideoType(mimeType)) return VIDEO;
+      return null;
+    }
   }
 }

src/org/thoughtcrime/securesms/mms/PartAuthority.java

@@ -76,4 +76,16 @@ public class PartAuthority {
     Uri uri = Uri.withAppendedPath(THUMB_CONTENT_URI, String.valueOf(attachmentId.getUniqueId()));
     return ContentUris.withAppendedId(uri, attachmentId.getRowId());
   }
+
+  public static boolean isLocalUri(final @NonNull Uri uri) {
+    int match = uriMatcher.match(uri);
+    switch (match) {
+    case PART_ROW:
+    case THUMB_ROW:
+    case PERSISTENT_ROW:
+    case SINGLE_USE_ROW:
+      return true;
+    }
+    return false;
+  }
 }