New GCM quickstart archetype

I have added a new archetype to the android-archetypes project that makes it possible to get a Google Cloud Messaging project setup easily.

It uses my GCMUtils library (https://code.google.com/p/gcmutils/) and therefore the amount of code generated is minimal and the configuration is very simple. By using this archetype you get all the config needed in the AndroidMainfest.xml file and also the setup required to send the registration id to your own server.

The required properties are (both are stored generated in the file assets/gcmutils.properties):
- sender-id (http://developer.android.com/google/gcm/gs.html#create-proj)
- gcm-receiver-url (url to your own server that will store the registration ids and send the messages)

I think it can be very useful to many people starting out with push messaging on Android.