Make identicons round

This commit renames identicons to avatars in field names, and uses an ImageView
derivative to show the identicons, which should make implementing #214 easier.

briar-android/src/im/delight/android/identicons/IdenticonDrawable.java

@@ -48,6 +48,16 @@ public class IdenticonDrawable extends Drawable {
         mDelegate.show(toShow);
     }
 
+    @Override
+    public int getIntrinsicHeight() {
+        return 200;
+    }
+
+    @Override
+    public int getIntrinsicWidth() {
+        return 200;
+    }
+
     @Override
     public void setBounds(Rect bounds) {
         super.setBounds(bounds);