Add support for a better cooperative threading model

As it stands today, the controller does nothing to help or hinder the use of threads. Going forward, some system to more carefully manage how threads are created and scheduled is likely to help overall system performance.

A good starting point would be to have a ThreadPoolService which OSGi bundles could depend on and then ask for new threads. The backing implementation could either just act as a blind passthrough to a java thread pool class or (in the future) could do something smart and have hierarchical thread pools with bins for containers, bundles or whatever.