Support audio attachments through GalleryMediaChooser

GalleryMediaChooser supports audio types also. It displays simple audio
icon and file info for audio files on grid views.

Test: Manual

Change-Id: I98b605156af3c1909c0141a2b99380b5da11c1e2
Signed-off-by: Taesu Lee <taesu82.lee@samsung.com>

tests/src/com/android/messaging/ui/mediapicker/GalleryGridItemViewTest.java

@@ -55,7 +55,7 @@ public class GalleryGridItemViewTest extends ViewTest<GalleryGridItemView> {
             final String imageUrl,
             final boolean showCheckbox,
             final boolean isSelected) {
-        final AsyncImageView imageView = (AsyncImageView) view.findViewById(R.id.image);
+        final AsyncImageView imageView = (AsyncImageView) view.findViewById(R.id.thumbnail);
         final CheckBox checkBox = (CheckBox) view.findViewById(R.id.checkbox);
 
         assertNotNull(imageView);