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.
* rewritten contact group support to support VCard3 CATEGORIES and VCard4-style KIND/MEMBER groups
* new account setting: contact group method (VCard3/VCard4/Apple "VCard4-as-VCard3")
* keep unknown properties when saving/generating VCards
* don't set ORGANIZER for events without attendees
* make some lists public final instead of @Getter private
* PermissionsActivity: call refresh in onResume() instead of onCreate()
* fix lint warnings
* line-break too long messages of network trace logs
* DebugInfoActivity "send": attach log file instead if sending it as plain text
* revert to ez-vcard 0.9.6 because of https://github.com/mangstadt/ez-vcard/issues/33
* German translations
* use VERSION_CODE and buildTime from BuildConfig
* new HTTP User-Agent, VCard PRODID values
* contact sync: store CTag in SyncState
* sync logic: upload contacts, check CTag, multiget