Fix #309 - NPE when database is empty on app update

* Move check for new app version to MainFragment.onActivityCreated(), so it is completed earlier in the Fragment lifecycle, before onStart().  onStart() connects to Google Play Services, so onConnected() (where we need to know if the app is a new version) can be triggered by callback from Google Play Services at any point after onStart().
* Reset OTPApp.PREFERENCE_KEY_SELECTED_SERVER if a new app version is detected in MainFragment.onActivityCreated()
* Check for the first execution of version_code 13 or higher, due to introduction of new OTPApp.PREFERENCE_KEY_APP_VERSION preference
* Bumps app version_code and version