moved.css to sass
refactored scm.css to sass
split css

- separated css for top_menu, header and breadcrumb
- started to remove double rules
added copyright notice for new scss, sass files
more css clean up

- moved all header section related rules to sperate files
- added sass_cache to gitignore
First changes for the openproject 3.0 layout
more css changes for the new layout
scroll whole page instead of of one container
fixed height of content div and footer position