util:
  - add randomSeed which raplaces Math.random with a seedable generator
  - colorStr: error check for alpha > 1 (i.e. 0-255 check)
  - rgbToHsb: return h,s,b in 0-255, not 0-1
  - hsbToRgb: input h,s,b in 0-255, not 0-1
  - sortBy: prop replaced by more general function, defaults to prop if string.
mouse: adjust to div being element, not name
models: test randomSeed