SLING-4217 - Register OSGi services corresponding to available adapter
factories

Extend the AdapterManagerImpl to register OSGi services for the adapter
factories that it manages. These services are unregistered when the
adapter factories themselves are unregistered.

git-svn-id: https://svn.apache.org/repos/asf/sling/trunk@1644110 13f79535-47bb-0310-9956-ffa450edef68