'Activate' Changes

[brendanthomas1]

Changes are allowed to (and probably should) be written before a feature is shipped. We should have some way to denote that a change is now 'active'

active_at attr and button that sets it from nil -> Time.current
days or duration column that says how long we should display this change as 'active' (or new?) (maybe active is a misnomer?)

(Maybe 'active' is that is just has been activated) (Current, new, recent, or something could be what we scope by?)

def current?
  active_at > Time.current - duration.days
end

Scoped index page for active (or whatever it's called) changes. This would ideally be for regular users to see new changes while the regular index page would be for admins. (how should show view be handled?)