Bug 1068366 - Update "Hidden devices" footer visual style in Remote Tabs home panel. r=trivial

The background colour was already correct.  This updates the text color
to match the mock, and adds a background selector that styles the footer
correctly when it is tapped.

mobile/android/base/resources/layout/home_remote_tabs_hidden_devices_footer.xml

@@ -18,9 +18,11 @@
     <TextView
         android:id="@+id/hidden_devices"
         style="@style/Widget.Home.ActionItem"
+        android:background="@drawable/action_bar_button"
         android:layout_width="match_parent"
         android:layout_height="match_parent"
         android:gravity="center"
-        android:maxLength="1024" />
+        android:maxLength="1024"
+        android:textColor="@color/home_text_color_disabled" />
 
 </LinearLayout>