added params check call for strong parameters

Added a call in `resource_params` to a controller method called `#{resource_key}_params` for retrieving whitelisted parameters. So for example in a users controller CanCan would retrieve the users parameter via the whitelisting method `user_params`, if defined.

I probably haven't considered all cases here. So this might be just a starting point for getting CanCan working with Rails 4. It works well in first tests I made.

What do you think?