Finished the GCM Server Aspect of the Donate-My-Stuff.
Added GCM HTTP Server - > DonateMyStuffHttpPushNotifier class...
Notify Servlet handles POST for new GCM registrations as well as
message-push requests.
For GCM, also added new class NotificationMessage which represents the
message to be sent out.
Also added PushNotificationRegistration which represents clients'
registrations with the GCM, and payload options are (0 - Reg, or 2 -
Send)

DonateMyStuffUtils - I have moved two helper methods to this utility
class. (1) the writeOutput method which writes out JSON responses, (2)
the getRawDataPayload method which is used to read POST data via
InputStream.