port to scss

actually this is a complete rewrite using parts from the
partly ported ypart theme. It changes some things which I thought
were bugs, e.g. blue links.

some things still need to be done:

*   3-level hierarchy in top navigation
*   test with geo branch
*   rm leftover files (e.g. images)
rm unused images
add grey box
geo
use original button color in some places
fix register button hover color
add new components to adhocracy.scss
center event stream icons
a11y: :focus everywhere :hover
rm uneccessary/conflicting css rules
fix new comment button color for light background
fix pager
Merge pull request #2 from liqd/feature-port-to-scss

port to scss