views.py: new function (remove_from_section) to remove a user from a section, using canvas_sdk
section_details.html:
 -- added ids to elements we need to find/manipulate via js
 -- added javascript to:
    call remove_from_section via ajax
    generate success and error messages based on ajax success/failure
    decrement count when user removed from section
    hide name range in header while deleting users
    display 'no users' message when count of users reaches 0
tests.py:
    added tests for remove_from_section
code changes from merge from develop
fix to views -- change to use response.json rather than using response.content
incorporated suggestions from code review
Merge pull request #77 from Harvard-University-iCommons/feature/Sections_CS

Feature/sections cs