Move dismiss calls for dialogs to onDestroy()

It was possible for a user to bypass the EULA by opening a recent
app, then switching back. Delaying the dismissal of the dialogs
to onDestroy() fixes the issue.

Signed-off-by: Greg Meiste <greg.meiste@gmail.com>
Switch to use GCM library inside Google Play Services. Closes #91

Signed-off-by: Greg Meiste <greg.meiste@gmail.com>
Replace semaphore with Object wait/notify

Signed-off-by: Greg Meiste <greg.meiste@gmail.com>