Dithering for clocks, etc

Thank you @andiohn for your feedback. If anyone is interested (in which of the two?), I could try to create clocks.

@Gordon thank you for your inspiration.

There are actually some options that might help you to do it without having to have separate images for each colour

It worked really well and looks almost the same: I use a 2 bit image with four colors. One color for the border of the number, one for the shadow at the top, one color for the inside of the number and one to be transparent. So it is possible to configure all color combinations that the users are interested in.

But what's the best way to change the colors on the fly? I don't think the suggestions from above work when we want to support mix colors and also transparency is needed because the numbers overlap.

I hoped there is some kind of callback that I could use when I pixel will be painted, but setCallback doesn't work for the existing "g".

Scanning the mapped image from storage and use g.setPixel seems very slow; I guess because on every call the display get's updated.

Currently the best approach seems copying the image from storage to make it editable, changing the pixels and then drawing it. But this is three loops (copying, modifying, drawing) where one should be enough.