I did some more frontend work!

1. i made the chessground rank/file responsive: for some reason, the default ones are positioned by pixel offsets and break pretty quickly on smaller screens. some light css max fixes this
2. recolored everything: stock chessground theme is kinda lame
3. made the time slider exponential: I wanted to give a larger time range (previous is 100ms-1000ms), but everything past 1s on the high end makes it really unwieldy to set the time on the low end, where people usually play. i made it exponential, i can expand the top end (3000ms now) without the slider feeling weird. it’s easier to show than explain