Side spectate on frontend too

[NBKelly]

ok I've done a couple of things here.

First:

• only actually compute the spectator diffs if there are spectators (or during a resync/watch/join event)
  That should actually cut out a lot of processing I think.

Second:

• If you're spectating as a specific side in an open-info game, flip the gameboard to that side
• If you're spectating as a specific side in an open-info game, you can see prompts

Hopefully that should feel more natural, and it should help testing groups (or people learning to play) to do so more naturally without needing to communicate in riddles.

Webm is a bit choppy because weyland doesn't update that contexts unless the window is in an active browser context (needed three of them to demo this).

output.webm