strongSwan

Currently we instanciate threads everywhere in the daemon. This makes capability dropping, proper thread shutdown and cleanup and module implementation tricky and unclear.

We want to provide a generic asynchron execution helper by introducing a "callback_job". This callback job gets a callback and is executed by the thread pool. This allows us to do all blocking activities in the daemon with these jobs.

Further we want to merge the job_queue/thread_pool into a single object: the processor. We do the same for the event_queue, it will be integrated into the scheduler for simplicity.