bump version to code 3 name 0.2.1
switching Contacts syncing to a timer set to 2 hours (closes #1763)

This should ultimately be replaced by a logic that only triggers the sync
when the GnuPG key list has changed.

https://developer.android.com/training/sync-adapters/running-sync-adapter.html

refs #1483
change URL in shared debug log to https://guardianproject.info/code/gnupg
added Polish translation (thanks SeniorEuhenio!)