adds banner images to and refines header on find courses pages, various visual tweeks and imporvements

Make rake clobber remote test_root/*_repo directories that are used and should be cleaned up by tests

Conflicts:
	common/lib/xmodule/xmodule/capa_module.py
	common/lib/xmodule/xmodule/modulestore/xml.py
	lms/djangoapps/courseware/views.py
	lms/templates/index.html
	lms/templates/info.html
	lms/templates/main.html
	lms/templates/navigation.html
	requirements.txt