VT UX Cleanup

Fixing two issues:
1. Contact photo shows behind video surface.  Refactored logic in
VideoCallPresenter to determine if video surfaces are showing/hidden and
call this from CallCardPresenter in order to determine if the contact
photo should be visible.
2. With contact photo hidden, background activities show through instead.
Added a black background color to the incall_screen to solve this.

Bug: 21192340
Change-Id: I45a88ba47ffa80f25bcee5b8d4f8e9b0de04f602
diff --git a/InCallUI/res/layout/incall_screen.xml b/InCallUI/res/layout/incall_screen.xml
index 9f75695..a772622 100644
--- a/InCallUI/res/layout/incall_screen.xml
+++ b/InCallUI/res/layout/incall_screen.xml
@@ -18,6 +18,7 @@
 <FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
     android:layout_width="match_parent"
     android:layout_height="match_parent"
+    android:background="@android:color/black"
     android:id="@+id/main" >
 
     <fragment android:name="com.android.incallui.CallCardFragment"