Add a "Move On" button to the end of both the answering and judging phases

These use the same voting style as the prompt voting, and allow the
game to proceed once a majority of players have voted to move on. This
should help avoid the game being locked out just because a single
player has decided not to play anymore, or somehow became disconnected
(which has already happened in practice more than once).

With this change, we're also now displaying the actual names of the
players that have already answered/judged (as opposed to just the
count as we were displaying previously). And we've written code to
also display the list of player names who are still in the
answering/judging process but that list is not yet being populated
(we'll need just a little more plumbing to have the client send an
activity ping to the server when typing/tapping/clicking before
submitting).