add directory layout for both local as well remote storage
use new layout for proxy and hosted repo
better naming and rounding up API
* removing the need ot RubyFSLocalRepositoryStorage for Hosted and Group repo

* moving common code to NexusLayout

* fixed DefaultProxy repo and reduced RubyFSLocalRepositoryStorage to minimum needed

* use RubygemsFile for group and implement first draft for merging DependencyFile
force uniq dependencies on merge
finalize bundler api improvements