Issue #84: starting to explore the hybrid configuration space ...

- so far it seems I might be able to keep Metacello out of this,
  which would be convenient at the moment the handling of the
  hybrid configuration for Metacello registrations is pretty much
  spot on ...
- hybird configuration is a configuration that loads a baseline
  from github (or filetree)
- basically the configuration is hanging onto the version (tag)
  and the repository where the configuration itself was loaded
  from ... the rest of the useful information comes from the
  baseline ...
Issue #84: more prep work

- push some more methods around so that the hybrid registration
  can do it's thing
Issue #84: finish off hybrid project implementation

- TDMetacelloRegistrationDefinition is now an abstract class
- move responsibilities into TDMetacelloRegistrationDefinition
  subclasses, so that hybrid project can provide proper
  behavior
- can now edit baseline or configuration from `project list`
Merge branch 'issue_84' into dev