Updated Android project to match latest SDKs

- Updated Parse Android SDK to 1.7.1
- Updated Facebook SDK to 3.19.1
- Updated Facebook login permissions: with the new Graph API v2.1, only
the "public_profile" and "email" permissions can be accessed without
sending the Fb app for review.
- Some code cleanup
Merge pull request #23 from alessandrofrancesconi/android-update

Updated Android project to match latest SDKs