Putting clear-all button on the right to match design.

- Moving Clear-all button on drop-target change
- Fixing issue with end-margin on title

Change-Id: I589425980cd4503275b33a555f3dcb8391ba2695

packages/SystemUI/res/layout/recents_stack_action_button.xml

@@ -18,7 +18,6 @@
     android:id="@+id/button"
     android:layout_width="wrap_content"
     android:layout_height="wrap_content"
-    android:gravity="start|center_vertical"
     android:paddingStart="14dp"
     android:paddingEnd="14dp"
     android:paddingTop="12dp"