Making VideoCastControllerActivity's UI a tiny bit more general

Now, if needed, developers can define an ImageView for the background image instead of the previous
background that was used for the layout. To do so, copy the cast_activit.xml from res/layout
to your own res/layout and update that by:
- add an ImageView
- remove the android:id="@+id/pageView" from the RelativeLayout and put it on your ImageView.
The rest will just work.
Fixed a number of bugs to avoid NPE in various cases
Fixing a possible flickering of notification when switching between activities
Many bug fixes and changes, please see the changelist fro 1.4 -> 1.5
Fixing an issue where VideoCastControllerActivity would show loading progressbar
If user started castinga video but lock the screen before playback started and
after playback started unlock the device, the loading progressbar was staying on the
screen.
Fixing issue #58
Addressed issues: #59, #61.
In addition, when in VideoCastControllerActivity, changing volume while video is
playing back will provide a visual feedback on the phone as well. This is to
conform with the latest recommendation in the UX Guidelines.
Adding logic to make sure that upon reconnection after a transient loss of connectivity,
the same app is running otherwise disconnect.
updating version
Updating gradle related items to get this working with Android Studio Beta
don't log loadMedia
fix AndroidManifest.xml
update build.gradle