Update to newer SCSS

This makes compass run, but contains erroneously styled buttons.

We should test the feature-port-to-scss branch in production instead and
make it the new master.
Merge branch 'feature-port-to-scss'

Conflicts:
	adhocracy/ypart_theme/static_src/stylesheets/adhocracy.scss
fix logo
fix register button
fix participate button color
fix original button color
mv twitter to footer and restore original login position
make footer links more responsive