Initial OSGI work

Towards BROOKLYN-13.
* Adds @ahgittin's initial work with Felix
* Updates catalog.xml to load and store bundle URLs under a `<libraries>` element.
* Adds helpers for loading classes from bundles to `BrooklynEntityClassResolver`
If we go with OSGi versioning we can use Felix's implementation of [org.osgi.framework.Version](http://www.osgi.org/javadoc/r5/core/org/osgi/framework/Version.html) class, which implements `Comparable<Version>`. There's also a `VersionRange` class.