Some code and documentation cleanup
course_wiki: Only search for groups with name containing course_slug minus underscore if the couse_slug prefix is numerical
course_wiki: Created seperate method to calculate course_wiki_slug
pylint fixes
Added check for old format groups
course_wiki: Course staff can manage/delete articles for their courses only; students cannot delete articles.
Refactored course_wiki/settings
course_wiki: Added tests for staff access
Cleaned up the tests