Colors: Cursor-navigating the palette should set fg/bg-colour

[humdingerb]

You can control the selected colour of the palette in the Colors window with the cursor keys. While it changes the colour of the big swatch in the Colors window, it does not change the actual fore- or background colour that's used on the canvas (and the preview swatches in the status bar there).

If you use the mouse to click on a colour, the left mouse button sets the foreground colour, the right sets the background colour.

Suggestion: normal cursor navigating sets the foreground, holding an additional modifier sets the background colour. SHIFT?