Verify relation-specific authorize and policy_scope calls

#### Context
There is currently no way to verify that a specific relation has `authorize` or `policy_scope` called on it. If you have `authorize` or `policy_scope` calls occuring more than once in any controller action, it does not ensure that any call after the first is actually happening. This pull request adds code that allows you to specify what classes you want `authorize`'d or `policy_scope`'d. It should not break existing code

``` ruby
class ApplicationController < ActionController::Base
  after_filter(except: index) { |c| c.verify_authorized(Post, ArticleTag) }
  after_filter(only: index) { |c| c.verify_policy_scoped(Post, Comment) }
end
```