This introduces a generic class called list_cursor to handle the
main details of navigating the buddy list and wires it into
activity.js. It replaces some fairly complicated code that
was coupled to stream_list and used lots of jQuery.
The new code interacts with the buddy_list API instead of jQuery
directly. It also persists the key across redraws, so we don't
lose our place when a focus ping happens or we type more characters.
Note that we no longer cycle to the top when we hit the bottom, or
vice versa. Cycling can be kind of an anti-feature when you want to
just lay on the arrow keys until they hit the end.
The changes to stream_list.js here do not affect the left sidebar;
they only remove code that was used for the right sidebar.
In this cleanup I make it so that all jQuery selector references
are toward the top of the module, and we do all finds relative
to the container ('#user_presences').
This will make it easier to make a better list abstraction for
the buddy list, for things like progressive rendering.
This change makes a common code path for these two operations:
* clicking on a user
* hitting enter when a user is highlighted
The newer codepath, for the enter key, had some differences that
were just confusing. For example, there's no need to open the
compose box, since that's already handled by the narrowing code.
For possibly dubious reasons, I let each handler still call
popovers.hide_all() on its own, since it makes the code a bit
more consistent with existing code patterns.