Consistent colours assigned to groups generated when subdividing tree

Jalview should not assign random colours when cutting trees.

Ideally, a standard scheme should be followed for colours selected for groups defined when subdividing the tree, and the colours should be applied in a consistent order (ie from one side (ie top) to bottom) get assigned colours red,yellow, green, orange, etc.

The legacy behaviour could be provided as an option, but for new users, the default should be to assign from a consistent palette.