Clean up footer implementation

[ramboz]

The footer will be implemented in Franklin so we need to review and clean up the existing footer we have and make sure it matches the current live one.

Advanced features will be handled separately:

• search via #110
• website feedback via #111 in https://github.com/hlxsites/delta/milestone/3, for now we can just put a link that redirects to the feedback page the same way it works for mobile

In particular, we need to make sure that layout, font sizes and all the links are working as expected