dropping legacy doorkeeper_for and welcome doorkeeper_authorize!

Details has discussed at PR #434

- dropped legacy `doorkeeper_for`
- new `doorkeeper_authorize!` method, let Rails` `before_filter`(perhaps `prepend_before_filter` is better) handle cases which resource need to be protect
- `includes_scope?` would force `to_s` for every given scope
Unused block argument - `v`. If it's necessary, use `_` or `_v` as an argument name to indicate that it won't be used.<br>Line is too long. [85/80]