Feature/sections css adjustments

Styles for home page to address usability issues found during testing.
Added icons for removing and adding users to a section.
Added tooltips to the icons on the section homepage.
Resolved conflict with Josies' commit.
I think it would read a little better if you just did `if section.enrollment_count` here rather than using the slugify filter.  I'm assuming that enrollment_count will either be 0 or > 0, so using truth testing would work.  When you do make then change, you'll just have to reverse the contents of the if/else.