Extract ORM specifics

rework of PR #454

ORM specifics except Active Record has extracted to [doorkeeper_bundle](https://github.com/jasl/doorkeeper_bundle) (not push to rubygems yet)
Right, that's part of "leaving specs unchanged" I guess. I'm ok with leaving the conditionals and ORM specifics in our tests, in exchange for not duplicating them across the gems/projects. I find it a good tradeoff.