[Proposal]: Footer should have it's own background colour setting, it's currently reusing a text colour

[MollyJameson]

Summary

Currently the footer style background is using $headingColour; which is described in _settings.scss as a Text colours.

I changed all the settings so I could have a dark mode but the footer really stands out. I modified the theme easily but this was still a bit confusing.

Proposed solution

Expose footer color in the settings or use on of the //Background colours settings