allow Header and/or Footer to be sticky without visual theme#119

I prefer to use the native theme from the site but I would like the option to make either the header and footer of the site to be fixed. **header** - You already have the option available but you are forced to use your visual theme. I'd like to decouple "sticky header" from the visual theme so you can use it in either case **footer** - One way to solve the issue of reaching the footer when infinite scroll is on is to make the footer position fixed to the bottom of the window. The current solution of reaching the footer is still not easy