Fix timing issues with user animations

It's easy to hit the millis() precision limit (4ms currently) when doing
fast user animations. Reduce the number of steps to ensure relatively
accurate timing.
Finishes to firmware

Remove randDots mode; there are too many already.
Add Spin mode, which looks cool!
Increase time per random mode from 10s to 15s
Start slowRainbow in a blue hue so monochromatic LEDs don't start off