Added ActionBarSherlock, Navigation Drawer, Integrated Index application, Implemented gmail login

Converted required activities to fragments for better integration of Navigation Drawer.
Moved old Home screen menu to Navigation Drawer. 
Index application is the new default screen after login. 
Gmail login uses oauth2 token obtained using google play services.
Additional external dependencies:
1. ActionBarSherlock
2. Google Play Services
Why do we need the invalidate here ?