NX-163: replace ClassWorlds with OSGi
Make OSGi API provided dependency (fixes signature mismatch when it appears before Felix on some test machines, see also https://issues.jboss.org/browse/WELD-1446)
Fix legacy IT restart issues caused by the JVM's caching of URLs that still refer to the shutdown framework instance
Extract BC provider as separate bundle in its own right so it passes the JVMs signature verification check
Auto-start plugin bundles (not required atm, but useful for the future)