database: Move all sorts of database operations into the main thread

database: Move all sorts of database operations into the main thread

We no longer support any database operations from any other thread than
the main thread (because otherwise we cannot figure out which Task we
are running in).

For that reason, we have to split a couple of tasks off at different
times and send blocking operations to an executor thread later.

Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>