Add ORM-specific loaders:
- lib\active_admin\orm\active_record
- lib\active_admin\orm\mongoid

Move comments to ActiveRecord ORM directory

Add ActiveRecord/Mongoid type checks to DisplayHelper#pretty_format(object) method
DisplayHelper#pretty_format fix indentation, remove nested if/else from case statement
Merge pull request #2545 from johnnyshields/orm-agnosticism

Make ActiveAdmin ORM agnostic (i.e. works without loading ActiveRecord)