Extracted equality operations in a separated module

 Some gems like [drapper](https://github.com/drapergem/draper) will include them self on `Mongoid::Document` and try to override the `==` operator, because mongoid defined `==` in the base class this is not possible.

 I've extracted all methods related to equality to a Equality module that is included in `Mongoid::Decoment` via `Mongoid::Components`