Implemented OSGi support for leshan server

Kai Hudalla, Ingo Schaal, Alexander Ellwein from Bosch Software Innovations implemented OSGi support for the leshan lwm2m Server.

The leshan-osgi module provides an OSGi-fied implementation of the ClientRegistry called OsgiBasedClientRegistry, which can be used inside an OSGi container as a OSGi service. The LWM2M clients are registered with this registry and can be controlled over it. There are also some integration tests based on Pax Exam test framework for testing the basic functionality.