Block sync adapter's onPerformSync until SyncWorker finishes (bitfireAT/davx5#278)

* Block sync framework until SyncWorker finishes

* Bump version code for 4.3.3 (previous version code was never released publicly)

* Fetch translations from Transifex

* Release internal version automatically [skip ci]

* Update periodic sync workers when "Sync only on WiFi" flag is changed (#282)

* Update periodic sync workers when "sync only on WiFi" flag is changed
* Remove BootCompletedReceiver which was only needed to repair sync intervals (not required with WorkManager anymore)

* Bump version code to 403030006 (stays 4.3.3)

* Use unique worker name, Java notify/wait and observeForever

* Remove observer when sync finished

* Catch and ignore, but log interruption exceptions

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Co-authored-by: Ricki Hirner <hirner@bitfire.at>