This is preferable to doing the way other QPs are passed (secret, etc) because
the link in the email wants to look like "#/room/<room_id_or_alias>" for guest
read-access (only bouncing you to /login if that room is not readable by guests).
This is hard to do in the current arch because we don't preserve QPs on /room
paths, and we do conditional executions depending on if it is a room ID or
alias. Rather than threading through the email in each section and creating
a fragile mess, just pass the *starting* set of query parameters through to
MatrixChat which can then do the Right Thing when the time comes.
