Better asynchronous loading for Recipient information.

1) Switch back from AsyncTasks to an Executor and Futures.

2) Make the Executor operate LIFO.

3) Make the Executor thread a BACKGROUND_PRIORITY thread.

src/org/thoughtcrime/securesms/util/Util.java

@@ -16,6 +16,10 @@
  */
 package org.thoughtcrime.securesms.util;
 
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.ThreadPoolExecutor;
+import java.util.concurrent.TimeUnit;
+
 public class Util {
 
   public static byte[] combine(byte[] one, byte[] two) {
@@ -62,6 +66,10 @@ public class Util {
     return splitString;
   }
 
+  public static ExecutorService newSingleThreadedLifoExecutor() {
+    return new ThreadPoolExecutor(1, 1, 0L, TimeUnit.MILLISECONDS, new LinkedBlockingLifoQueue<Runnable>());
+  }
+
   //  public static Bitmap loadScaledBitmap(InputStream src, int targetWidth, int targetHeight) {
   //    return BitmapFactory.decodeStream(src);
   ////  BitmapFactory.Options options = new BitmapFactory.Options();