Include source origin in string key name.

This should help eliminate string duplicates, as well as provide
visibility into where strings in a resource file are being used.

res/layout/conversation_fragment_cab.xml

@@ -8,7 +8,7 @@
 
     <TextView
         android:id="@+id/title"
-        android:text="@string/batch_selection_mode"
+        android:text="@string/conversation_fragment_cab__batch_selection_mode"
         android:maxLines="1"
         android:singleLine="true"
         android:layout_gravity="center_vertical"