Check for unscoped model finds

Adds a simple check for unscoped calls to `#find` on models that belong to other models. For example, if `Email` belongs to `User`, calling `Email.find params[:email_id]` should probably be `some_user.emails.find params[:email_id]` or similar.

The confidence on this will always be low since this kind of find may be intentional. It may be too false positive heavy to be worthwhile.

/cc @gregose @ptoomey3 
Since you are not doing anything with the results of `has_immediate_user_input?` or `has_immediate_model`, you could just use `include_user_input?`.

Also, please use the result of `include_user_input` to set the `:user_input` value in the warning, like `:user_input => result.match`.

Thanks!