Enable source attachments on libraries in 'Bnd Bundle Classpath'

The commit supports storing source attachment data (if there is any) for each library exposed via the BndClasspathContainer. The attachment paths are persisted to a properties file per project within the plugin storage location.

There is also primitive support for eclipse style bundle source attachement. Given there are a lot of bundles that have source attachments that follow <bsn>.source I have included the ability to find these bundles from the repositories and auto wire the source attachments up.

It may well be there is a better approach for doing this, my experiences with eclipse plugin development is somewhat limited.

I am open to suggestions for ways to improve it, whatever that be.