Allow form components to be shown/hidden in groups

Each component gets a `group` property (a grouping name).
Giving components the same `group` puts them in the same grouping.
The `form_card` gets something like an `active_group`, which only shows components that belong to that grouping.

This makes it easier (and lazy/mis-usable) to use tabs without having to remember state across each tab.

Related to #136