Resolves to TODOs in the doorkeeper for helper

Moves token validation from DoorkeeperFor class into the Access Token
class.
Add specs for new methods in AccessToken and Scopes

adds test for includes_scope? acceptable?
Fix a style error in specs
Remove duplicated valid_token? method
allow to contain a query parameter
Update CHANGELOG. [ci skip]
Controllers refactors:

* Remove empty methods
* Extracts methods in AuthorizationsController
* Comment adjustment
Failing test for issue 398
Native redirect for implicit token grant bugfix

See: https://github.com/doorkeeper-gem/doorkeeper/issues/398
Moves from update_column to update_attribute

Ensures cross-ORM compatibility.
Removes Revocable module trails
Update CHANGELOG. README TOC update. [ci skip]