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`
`loadClass(type)` will throw `ClassNotFoundException` if not found.
Better to just catch that rather than generic Exception?
e.g. if bundle name was invalid then fine to throw exception rather than just returning `Maybe.absent()`.