dispatching mechanism in UrlHistoryController

currently just handles initial sign-in
usersignin dispatches to home
landing page and back button work
should call them "panels" instead of "tabs"
back and forward buttons work
some more documentation (still incomplete)
listen for initSearch event to add/remove panels in URL

better than putting URL logic in multiple controller methods
forgot to actually add token to URL
didn't do that right, for various reasons
fixed close button bug
use newSlice event instead to capture panel updates
window controls refactored into windowing controller; panel update works
update on widget change
all seems to be working

fixes #33
enter key submits form
dispatch initial hash (on direct link or reload)

bypass sign-in process for now since it’s going to change anyway.