Align timers

[shish]

browser2 and player2 update state once per second, starting from when the page is loaded

If the projector is loaded at 00:00.000 and the podium is loaded at 00:00.500, then there will be a constant half-second lag as the podium only reacts to updates half a second after the projector reacts

It'd be good to have some way to say "call the update function once per second, exactly at the moment the second changes"

[shish]

Also setInterval() can drift...

Maybe we need a custom timer of setTimeout(round_up_to_next_second - now())