Remove obsolete RegisteredClientRessource, improve error handling on
client registration
Adopt changes made earlier to new improvements branch
Refactor code into separate Maven modules
Add a module providing support for OSGi Device Access
Use managed version of commons-io
Merge latest changes from master
Merge branch 'improvements' of github.com:sophokles73/leshan into sophokles73-improvements

Conflicts:
	src/main/java/leshan/server/lwm2m/resource/RegisterResource.java