Less ridiculous helpers

This PR will remove that long list of rails helpers. Unfortunately I couldn't figure out a way to do the same thing for the form helpers, but hey, it's an improvement.

Oh, and I added native support for [SimpleForm](https://github.com/plataformatec/simple_form) while i was at it. If this becomes a supported fork of Erector, that code should probably go in the SimpleForm repo instead of in here.