Implement new media send flow.

Update our media send flow to allow users to send multiple images/videos
at once. This change includes:

- New in-app media picker flow.
- Ability to caption images and videos.
- Image editing tools are made more prominent in the flow.
- Some fixes to the image editing tools.

src/org/thoughtcrime/securesms/components/ControllableViewPager.java

@@ -7,10 +7,12 @@ import android.support.v4.view.ViewPager;
 import android.util.AttributeSet;
 import android.view.MotionEvent;
 
+import org.thoughtcrime.securesms.components.viewpager.HackyViewPager;
+
 /**
  * An implementation of {@link ViewPager} that disables swiping when the view is disabled.
  */
-public class ControllableViewPager extends ViewPager {
+public class ControllableViewPager extends HackyViewPager {
 
   public ControllableViewPager(@NonNull Context context) {
     super(context);