This commit includes the major changes between DAVdroid and EteSync. It
adjusts the app to use the EteSync protocol and server. It includes some
ugliness still, and it's a squash of many ugly snapshot commits while
hacking on the initial DAVdroid code.
History should be "clean" from this point onwards.
* allow ProGuard optimization to remove non-relevant bytecode from flavors
* check flavors with direct comparison instead of .equals() to allwo optimizations
* store cookies per HttpClient, and not per DAVdroid instance (allows multiple sessions for parallel syncs)
* fetch translations from Transifex
* add startup dialogs (F-Droid: donations, Play Store: DRM bug, OpenTasks not installed)
* allow to reset hints/startup dialogs
* AccountSettings: fragment as inner class of activity
* move AccountSettings up to package context
* HttpClient: take authentication from AccountSettings in the constructor
* App: provide global instance of MemorizingTrustManager
* App: provide global Java logger, optionally with verbose and external file logging
* LoginCredentials: moved from inner-class into setup package
