fix Rails 4 problem with form builder ("undefined method `upcase'")

In Rails 4, ActiveRecord::Base#model_name no longer returns a string, but an ActiveModel::Name object, see https://gist.github.com/brupm/4544950. Calling #to_s on this object is a Rails3-compatible workaround for this change.
starting to integrate changes for #2002
adding the changes for locales #2002
updating test #2002
fixing the dropdown issue #2002
moving the validation to the correct method in forms.rb #2002
testing a no change commit #2002
fixing the language dupe issue #2002
updating the string filter to use the new module #2002