Diversify block colours

[Alzter]

I feel that a lot of the block colours look too similar. Events, Control, Variables and Custom all look too close together, and Motion and Sensing also look quite similar. So I made my own mock-up comparing 2.0, 3.0, and my own set of block colours that I think look better than them both.

I tried to keep the saturated look of 3.0 but made the colours stand out and not blend together.

[towerofnix]

See also scratchfoundation/scratch-blocks#1032 and scratchfoundation/scratch-blocks#995.

[thisandagain]

Tracking in scratchfoundation/scratch-blocks#995