New inline color plugin

[RunDevelopment]

Motivation
Most editors these days show you an inline preview for colors. E.g.

(VSCode)

Description
For now, the new plugin should show an inline preview for every CSS color value like in the above screenshot. The box should be non-selectable and has to be exactly 2 characters wide to keep all characters of monospaced fonts aligned.

This can then be expanded to other styling languages (Less, Sass, Stylus, ...).

Alternatives
This could also be part of the Previewers plugin but I think that the Previewers plugin is complex enough already and I don't like the idea of having the load the heavy Previewers plugin just to get some inline colors.