Now push message is only displayed once

- When the user goes back to the activity opened by the push, the message is not shown again.
- Also, the code is refactored: we don't need the receiver.
- The code needed by the user is simpler (we will update the documentation):
  - onCreate: nothing
  - onResume: register and check pushes (I think register could better go in onCreate)
  - onNewIntent: setIntent(intent)
  - onDestroy: GCMRegistrar.onDestroy (we will add a MalcomLib method for this)

  Also, fix in the beacon url: beaconURL = "v1/beacon"
Little fix in javadoc
Merge pull request #7 from MyMalcom/bug-push-message-displayed-when-go-back-to-activity

Bug push message displayed when go back to activity