Add function in user-groups.py for getting member ids
for a group.
Update view to enforce checks for modifying user-groups.
Only admins and user group members can modify user-groups.
Previously, we weren't doing a proper left join in
user_groups_in_realm_serialized, resulting in empty user groups being
excluded from the query. We want to leave decisions about excluding
empty user groups to the UI layer, so we include these here.
This adds the data model and bugdown support for the new UserGroup
mention feature.
Before it'll be fully operational, we'll still need:
* A backend API for making these.
* A UI for interacting with that API.
* Typeahead on the frontend.
* CSS to make them look pretty and see who's in them.
Tarun Kumar
Tim Abbott
rht
Umair Khan