Our client code will now receive avatar_url in
page_params.people_list during page load, so it will be
able to use more current urls for old messages (the client
already had some logic for that and was just missing the
data).
We also add avatar_url to the realm_user/add event.
When we change the avatar, we make sure to always send a
realm_user/update event (even for bots).
We also needed to add avatar_version and
avatar_source to our active users cache.
The original include_subscribers implementation did not correctly
update the apply_events code path to avoid adding 'subscribers' dicts
to things. This corrects that oversight.
There's a new option, `include_subscribers`, that controls whether the
API sends down subscriber data for the various streams you are
subscribed to.
This has significant performance savings for large realms with naive
clients, and saves a bunch of bandwidth as well.
This moves do_events_register, fetch_initial_state_data and friends to
a new file.
Modified significantly by tabbott for correctness and to remove unused
imports.
Fixes#3635.