WET Theme: Footer, menu and background

@thomasgohard I changed the colours for the footer, menu and background. I will work on the next PRs. Let me know if I'm doing something wrong. It has been a while since I made my first pull request. 


Changing the selector to `footer` means this will be applied to all `<footer>` elements, not just the site footer. If this is supposed to apply to the site footer, use `#wb-info` to target the site footer.