Feature/sections tool sm2

This pull request contains changes for delete section" 
- added remove_section method that uses canvas_sdk
-prevent primary sections from being deleted
- added ajax call to UI to handle 
    *hide the deleted row on success
    * display success and failure message
    * display special message when primary section is attempted to deleted(even though UI doesn't have a delete for primary sections)
- unit tests
- UI has a 2 delete icons as placeholder -one for deletable sections and a disabled one when member count >0

I did try that as I have used it elsewhere. But the values didn't get passed in properly within the javascript block . I had it working with one param in  ajax url at line 385 as
url: {% url 'ap:remove_section' sec_id %}+sec_id
 but had to append values after the trailing }. And when I needed the second parameter, it broke.