logthrdestdrv: make the thread ivykis based.

It is easier to add timer, task, event etc. to the threaded destination,
and this re-factorizing eliminates the locking and waiting for conditions.
And the throttle timeout handling is also added to logthreaded destination.

Make this code is more maintainable.

Signed-off-by: Juhász Viktor <viktor.juhasz@balabit.com>