FELIX-4252 Make Extender's ThreadPool size configurable

* Oops, forgot to register my service under ManagedService interface ...

git-svn-id: https://svn.apache.org/repos/asf/felix/trunk@1527960 13f79535-47bb-0310-9956-ffa450edef68
Removed unused field

git-svn-id: https://svn.apache.org/repos/asf/felix/trunk@1527961 13f79535-47bb-0310-9956-ffa450edef68