Created mongoid adapter and models, adjusted tests to work with it.
Changes to adapters
Moved setting class defaults to a private class method.
Fixed all tests to work with both AR and mongoid3
Merge branch 'master' into mongoid

Conflicts:
	lib/public_activity/config.rb
	test/test_helper.rb
	test/test_tracking.rb
fix additional attributes for AR
fix custom fields for mongoid adapter