Fixes “DeprecationWarning: 'jinja2.Markup' is deprecated and will be
removed in Jinja 3.1. Import 'markupsafe.Markup' instead.”
Signed-off-by: Anders Kaseorg <anders@zulip.com>
It is confusing to have the plan type constants not be namespaced
by the thing they represent. We already have a namespacing
convention in place for constants, so we should use it for
Realm.plan_type as well.
Moving forward we are hoping to collect data on org types from our
users, so it makes sense to display the org type on the "Counts"
tab of our /activity page.