Added the ability to merge manifest files from library project

Finally, the new ADT tools allow us to merge ```AndroidManifest.xml``` from library projects.

Summary of changes:

* Pulled out all the SDK activities and services from the app manifest files to the SDK's manifest file.
* Modified ```project.properties``` to allow merging of manifest files.

This helps us going forward, as we add more activities and services (new service for push coming up).