Feature/section tool cs

Refactored add people tool to open directly in 'Manage Sections' page when navigation link is clicked
Removed the cap_top template, which was the previous landing page for the tool
Views.py:
-renamed cap_top function to ap_top (minor - 'cap' dates from when the project was named 'course add people' rather than 'add_people')
-modified ap_top to redirect directly to create_section_form ('Manage Sections' landing page) rather than    -cap_top for success and appropriate errors
-tool_config modified to default to 'Manage Sections' for menu link text

Urls.py:
changed cap_top to ap_top

create_section_form.html:
transferred error message block which had been in cap_top.html   

tests.py 
Modified one success test; added another
This view function seems to exist solely to check for the existence and validity of the course instance id and then redirect to the form view or render the form view in an error case.  Instead of separating this logic out and relying on a redirect, I'd consider moving this code into the create_section_form view code itself.