Adding global WP.com account. Refs #496

 * Credentials are stored in Preferences and uses the existing
encryption methods for the password.
 * Incremented db version and added migration script that attempt to
migrate the WP.com credentials from the first matching WP.com blog.
 * Added basic GCM setup. App ID needs to be added to the
config.properties in res/raw as gcm.id
 * Added WordPress.com section to preferences, and added capability for
!AddAccountActivity to be used as a WordPress.com authenticator of
sorts.
Adding basic GCM Service Class for testing
Moving activity restore code to PostsActivity

Having this in WPActionBarActivity would cause any new activity to close itself if it wasn't a menu item activity.
Adding refresh menu bar item to NotificationsActivity