Visual state of sectors

[nazar-pc]

I have some interesting ideas about UI of the plot:

• render it as a grid of small squares, each representing a single sector (like contributions on GitHub)
• sector color depends on whether it is not plotted (gray), plotted (blue), about to be replotted (yellow) or expired (red)
• sector that farmer is working on (plotting or replotting) will be blinking green, showing what farmer is doing