Adding transient messages support and universal links support

Add support for sending messages marked as transient

Added new API that overloads the existing sendMessage() API with an additional parameter 'isTransient'. The new flag allows the device to skip processing of the sent message if the volume of the messages from the companion app is too high.

Add support for UniversalLinks to open the example app

Instead of using URLScheme to let the GCM open the example app attempt to use the universal links to open it.

1.5.2

Several bug fixes and code improvements.