Tag IDs must exclude values like "id"

[boblail]

IDs for all FT fields should be underscored versions of the name of the field --- like Rails' FormBuilder IDs

[boblail]

Currently, my overrides of FormBuilder.hidden_field doesn't have ID fields.

The reason for that override --- a better way to describe hidden arrays --- might no longer be necessary.

Look into a refactor that relies more heavily on super.