This commit allows the user to set their preference vis-a-vis
the chat icon in the header of the page. There are three options:
- All New (default) - This maintains the existing behaviour where
all new messages in the channel show a blue dot on the icon
- Direct Messages and Mentions - Only show the green dot on the
icon when you are directly messaged or mentioned, the blue dot
is never shown
- Never - Never show any dot on the chat icon, for those who
want tractor-beam-laser-focus
