Android cleanup

Changes to the Android client. I verified that it runs on a genymotion simulator and a Nexus 7

@oalami Please review.

- Upgraded to Firebase v2
- Upgraded Gradle to most recent version

- Removed some dead code
- Added ability to select 'none' as a floor
- Removed some abuse of RuntimeExceptions and replaced with proper logging and user routing
- Fixed code style issues
- Extracted some strings