Make some improvements to the mobile web layout:
* The Who List button now will always be on the top right corner of conversation
threads, including when you are in a DM. This makes navigating easier as you
don't need to leave your DM and return to a public channel before being able
to access the Who List.
* In the top panel for DM threads, remove the Profile and Close buttons. Instead,
the Close button will be on the DM itself on the Channels list.
* When you are in a DM thread, and your chat partner is on camera, their camera
button will appear in the title bar for easy access and visibility.
* In a DM thread, clicking the username in the chat title bar will open their
profile card.
Apparently some iPad browsers were having their local webcam freeze
after a window.confirm prompt was shown. This replaces all uses of
window.confirm/window.alert with an in-app modal.
