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)
Might be better to change `rescue` to `ensure` and then replace `fail e` with:
```ruby
puts "Doorkeeper: ORM adapter not found (#{configuration.orm}). You probably need to add the related gem."
```

As otherwise this rescue hides any errors with the ORM / the real error and is confusing