Move controller logic into a module, for great mixinability

Judge::Controller can be included in any controller now, to turn that controller
into an endpoint for AJAX validations. The helper method for building a validation
from given request params was moved into there too, as this is probably where
that logic belongs.
Remove HTML module and simplify Judge::FormBuilder

Having the data-validate attributes generated by a separate module was
gratuitous. We're now also no longer checking for options[:validate] in every
FormBuilder method. #add_validate_attr! checks the options and add the data attr
when it's needed.