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.
* increase target API level to 23 (Android 6), which makes Android 6-style permissions mandatory
* AUTHENTICATE_ACCOUNTS permission is only required up to API level 22
* new activity: PermissionsActivity which shows missing permissions and provides buttons to request them
* DavService: Android shouldn't send a null Intent, but sometimes it does, so implement null check
* LocalTaskList: tasksProviderAvailable may return true on API level 23+ even if permissions are not sufficient
* SyncAdapterService: show a notification (with Intent for PermissionsActivity) when permissions are not sufficient
* when creating accounts, set OpenTasks sync always to true if API level is 23+ (even if OpenTasks is not installed [yet])
* update Lombok
* new setting: only sync in WiFi (or when sync is triggered manually)
* new setting: only sync in specific WiFI (by SSID)
* lower default sync interval when account is created to 4 hours (was 1 day)
* version bump to 1.0.6
* AccountSettings$AppUpdatedReceiver: check for migrations only when package is replaced
* SyncAdapter: move DB helper from service to SyncAdapter to prevent databases from being closed too early
* Manual sync button: run sync immediately (without queueing)
* add InvalidAccountException for invalid (=not existent/invalid settings version) accounts
* handle invalid accounts properly
* HttpClient: add constructors without Account when authentication is not needed
* drop upgrade compatibility for accounts without version (version<1)
Tom Hacohen