Generic Repository Browser component

[jng]

The Live Map Editor requires some means of browsing the current repository. We have most of this logic in place in the ResourcePicker class, so we should refactor this functionality by extracting it out into a re-usable control.

The SiteExplorer class is more comprehensive (and supports multiple selections, and site connections), but requires greater effort to un-tangle from the Maestro add-in infrastructure for external use