add base classes so its easy to add a custom ProjectType using a set of maven archetype coordinates

on the iPaaS we've a few archetypes we'd like to move to a top level ProjectType so it'd be nice to write a few helper classes so its easy to setup a ProjectType for a specific archetype instance. So folks have the choice of picking any archetype in the list of catalogs; or picking one of the pre-chosen top level archetypes.

Have got this working; its a minor refactor and a couple of helper classes so will submit a PR shortly!