add folder option to sidebar styling
remove whitespace
minimized folder keeps the gray color
use with with opacity instead of specific colors

toc-color-light is still in use elsewhere, so leaving it in
Merge branch 'master' into atc-sidebar-folder-styling

Conflicts:
	styles/variables.less
Merge pull request #98 from oerpub/atc-sidebar-folder-styling

Atc sidebar folder styling