fix(form-group): update margins & support static forms

CI had some issues without margin-bottom for .form-group.

This keeps the default .form-group margins and adds support for .form-horizontal-static to enable detail page type styles with form-group's. Might be a breaking change for people depending on this but it's nothing disastrous.
Also, even if there is a bottom margin, it seems like we should just let the margins collapse.