Colour moles for distinctiveness in set, not uuid, in 'mel rotomap-{edit,view}'

[aevri]

Colours are currently picked based on the uuid of moles. There are inevitably co-incidences where the colours picked are the same or similar.

It doesn't seem to be so useful for moles to have a consistently chosen colour between runs of commands - they are not particularly memorable.

If we're free to choose arbitrary colours then perhaps instead we can choose colours based on the limited number of moles available from the arguments passed to rotomap-view and rotomap-edit.

Perhaps we can use a different colouring schemes depending on the number of moles to colour, taking advantage of more distinct palettes when the number is low.