Twit 03 view pager and fragments

Creates a view pager and migrates all activities to fragments. Authentication Manager has been refactored into the authentication fragment, to prevent lots callbacks.

![authenticationmenu](https://cloud.githubusercontent.com/assets/3380092/3855378/e9be7c2a-1ee3-11e4-9897-3c9a07d58463.png)
![viewpager](https://cloud.githubusercontent.com/assets/3380092/3855384/f066ba2e-1ee3-11e4-8124-92af39a6d7b8.png)

to re-write my comment in english as I was in a rush :tongue: :

`requestAccessToken(String)` will (should) only be called at an appropriate time; i.e. triggered by something on the AuthenticationFragment? If it's called when the AuthenticationFragment is not available, then it does nothing, and there's no error or indication something went wrong -> should it throw DeveloperError if it's _not_ the `AuthenticationFragment`?