strong parameter support refined to allow standard Rails 4 notation

This commit allows one to use standard rails 4 `params.require().permit()` notation.
It's done in such a way that this doesn't clash with `permitted_params` if it's already defined. But if it doesn't, then default `permitted_params` falls back to a permitting method with resource-specific name.
Method user should define is the same as scaffold generates and thus the same as other gems such as cancan will try to handle.