Enable user to set persistent colorScheme for the whole website

[Letme]

Sometimes you do not want to present user a dark or light color scheme, but you decide on one (for example dark metal bands, I doubt they want to have light color scheme, or some church a dark scheme). In such cases it would be good to provide a website administrator option to set persistent color scheme. That way the colorScheme selection feature becomes optional, but default color scheme is still respected by the template.