Add an editor window color project setting

Created by: Calinou

This can be used to distinguish projects more easily, which is especially helpful when working on multiple projects at the same time.

The current coloring is a proof of concept. It does the job, but it's not that pretty. It'd be ideal if we could change the window border colors, but this requires us to implement client-side decorations first. (In other words, disabling the system-provided window borders and adding our own.)

This feature is inspired by the Visual Studio Code add-on Peacock.

Preview