Handle all CSS system colors

[dilyanpalauzov]

A SVG file can contain the colors Canvas, CanvasText. These depend on the current light/dark preference.

This library shall utilize the CSS System Colors, apart from the currentColor.

[mueller-ma]

@dilyanpalauzov supplied a SVG with CanvasText in openhab/openhab-android#3364 (comment).

At least Firefox uses the same color for CanvasText as for CurrentColor. Maybe it's enough to handle CanvasText as an alias of CurrentColor?