Maintenance Thread

Closes #51 (closed)

Important

CDI seems to have a hell of a bug where accessing the @ApplicationScoped registry blocks execution forever. When the registry was a @Singleton before, this issue did not exist. I tried making the registry @Singleton again and serializable, but this did not work. Therefore, I had to apply this super-ugly fix you find in the latest commit. Now at least shutdown works properly, because actually for over a week our app did not shutdown correctly but was at some point forcefully terminated. You can see this by not having any log output, which is now there again.

@all Please, look into this as maybe I just was too dumb to find a nicer solution. This seems to be totally fucked up.