Most of this code was simply moved from activity.js with some
minor renaming of functions like set_presence_info -> set_info.
Some functions were slightly nontrivial extractions:
is_not_offline:
came from activity.huddle_fraction_present
get_status/get_mobile:
simple getters
set_user_status:
partial extraction from activity.set_user_status
last_active_date:
pulled out of admin.js code
We also fixed activity.filter_and_sort to take user_ids.
Steve Howell