Reorganize information in CONTRIBUTING.rst, link to ReadTheDocs
Remove google analytics tracking from iframes used in Drupal course about pages

This fixes two issues:
 - if the course pointed to doesn't exist, GA was added to the iframe twice
 - more importantly, we don't want to count these as separate views anyway--
   we just care about the about page itself.
 - I also added a note about where we would put our segment.io widget if we want it
   later

LMS-2581
wordsmithing
Add admin.py for instructor_task.

This is primarily so that we can manually fail zombie instructor
tasks that are clogging up the queue for a course.
fixes firefox image hidden overflow bug.
puts GA id in quotes
Disable draft and edit links during ajax calls
STUD-1485
STUD-1499
Merge pull request #3274 from edx/ormsbee/instructor_task_admin_for_daves_vacation_enjoyment

Add admin.py for instructor_task.
Merge pull request #3560 from edx/adam/disable-links-ajax-2

Disable draft and edit links during ajax calls
Merge pull request #3564 from edx/adam-fix-GA-quotes

puts GA id in quotes
Make release table by PR, instead of by commit
Merge pull request #3551 from edx/victor/remove-iframe-ga

Remove google analytics tracking from iframes used in Drupal course abou...
When sending bulk email check if course is authorized.
Also the idash_mode property is stored seperately for each course.

LMS-2565
Update IFrame documentation
Merge pull request #3527 from edx/sylvia/docs/DOC-295

Add IFrame template documentation
Parameter from_email to send_mail() should be string and not string in list.

LMS-2518
Major refactoring based on Cale's branch approach
Fixed link to docs.edx.org in readme
Removed unused function
removed unused import