Fix CongressMessage#common_fields

[esoterik]

Due to forcing some congress forms fields to be "always common" (e.g. showing up at the top of the form and being sent to the controller as common fields), fields with mismatching options_hash values (such as using state abbreviations instead of full state names in addresses) still get grouped together.

We should figure out a more consistent way of sharing the common fields between the controller and the congress message.