Use `Mongoid::Matchers#matches?` instead of  a database query in `MongoidAdapter#matches_conditions_hash?`

allow model adapter to override condition hash matching in Rule, also clean up Mongoid adapter and specs

Automatically add `accessible_by` to Mongoid Documents to match CanCan behavior for ActiveRecord and DataMapper.

Previously, CanCan::ModelAdditions had to be included in each and every Mongoid document separately. Also removed manual include of CanCan::ModelAdditions from Mongoid documents in Mongoid adapter specs.

removing Mongoid::Components hack, tests are passing without it, add tests if this is actually needed