Add touch feedback and focus on Dashboard tiles

- use a touch-feedback background
- declare DashboardTileView as focusable

Change-Id: I67ae19cd20374e531660232034528c995f595900
diff --git a/res/layout/dashboard_tile.xml b/res/layout/dashboard_tile.xml
index 03b4b09..7b61d17 100644
--- a/res/layout/dashboard_tile.xml
+++ b/res/layout/dashboard_tile.xml
@@ -19,8 +19,7 @@
         android:layout_width="match_parent"
         android:layout_height="match_parent"
         android:gravity="center_vertical"
-        android:minHeight="72dp"
-        android:background="@android:color/white">
+        android:minHeight="72dp" >
 
     <ImageView
             android:id="@+id/icon"