Third iteration:

Fix broken scrolling (and incorrect positioning of quad tree lines) by
serializing the SpaceMapper(-transform) from take_context, and using it
to transform the primitive rects (instead of the previous translation
based on unclipped.origin);
Note: this is done at visualization time and not at export time to
distinguish actually moving elements from merely-scrolling ones.

Serialize the entire UpdateList, so we get the data (Keys) that's being
added; add it to the overview;

Move the static CSS code into tilecache_base.css; add this and the .js
file to the binary, write them as part of output (instead of manual
copy); clean up CSS a bit;