Choose and implement a color scheme

An initial state. You can play a bit with it by commenting in and out the colour palettes in colours.less (and shuffling colour numbers) and recompiling (`./scripts/compile-css.sh`).

Additionally I have switched from `recess` to `lessc` to compile less files (`recess --compile` is just a wrapper around `lessc` and I've found it limits command-line options and obscures error messages).