Change approach to layout in order to fix some weird CSS problems

Move away from using an absolute positioned #content div as this was
causing some weird problems when users scrolled down, like not showing
bottom padding, and prematurely cutting off the left keyline.

Now, the content area uses relative positioning most of the time, and
fixed positioning when the full screen map is in place.

Using fixed positioning on the big map is nice because you can now scroll
down to see more sidebar content, but you won't end up with an ugly block
of white space under the map.