Feature/sections add5 cs

add users to section functionality added:
add_to_section function added
javascript for add_to_section
template addition and modifications to fascilitate independent refresh of left and right panes
left and right sides stay in sync between add and delete operations
added enroll_count to the return of section_class_list
unit tests added
added double click protection to add user 

Is it necessary to load the list of users after the page is rendered, instead of coming back with the list already populated in the template?  If the concern is that you'd have two view functions doing the same thing and that you'd have to recreate unit tests, etc. then a possible solution is to do something like the following in the existing section details function:
`if request.is_ajax():
    render(... # HTML snippet or JSON
else:
    render(... # Full HTML template`