New solution for unique field update

Ok, this is the alternate solution for Issue https://github.com/philipbrown/magniloquent/issues/22. I added a private function that checks if a :ignore_id: value is present on a unique rule. If the columnId is present that is used, if not it uses the default column name id.

Notice that it doesn't work if you need and id that is not in a column of the table of the current model, but I couldn't think a situation where you could need that.