AC-727
began changing colors in course content, files and uploads, and when creating a course
finished fixing contrast issues on files and uploads page
fixed advanced settings and issue with hovering in files and uploads
fixed color issues in studio home page and when hovering
fixed contrast in updates, pages, textbooks, and group configurations
fixed issues when configuring a section of a course in course outline
fixed hovering colors to make contrast more visible
fixed colors on the green button
AC-727
2. Update COMPREHNSIVE_THEME_DIR to COMPREHENSIVE_THEME_DIRS
3. Update paver commands to support multi theme dirs
4. Updating template loaders
5. Add ENABLE_COMPREHENSIVE_THEMING flag to enable or disable theming via settings
6. Update tests
7. Add backward compatibility for COMPREHEHNSIVE_THEME_DIR
