show graded content block without the upsell when the upgrade deadline is expired

Removed one-off management commands.

Check course start and end dates, better test coverage

BOM-593

BOM-627

BOM-729

Add transformer for re-writing video urls in course api

BOM-595

BOM-742

BOM-741

BOM-739

BOM-421

Prevent unicode error

BOM-671

BOM-612

Division changed in python3 to produce floats even when you divide tw…

EDUCATOR-4696 readded get_history

EDUCATOR-4696 - put back get_history and update UI

add pylint

Finally import courseware properly everywhere to get rid of a warning

NullTranslations object doesn't have ugettext attribute

SE-1463 add djangoapps.heartbeat to INSTALLED_APPS by default

BOM-614: AssertionError: Lists differ Fix. 

Some of the tests are failing because NullTranslations object is
behaving differently with py2 and py3.With py2, it has 'ugettext'
attribute but with py3 it doesn't have.To make it compliant with
both versions modifications in the tests have been added so that
build will not fail.

PROD-663

Use order date_placed enrollment attribute for refund.

Studio Component Editor Tweaks

* Enlarges component modal for easier editing
* Allows display name to be edited in place
* Improves markdown button labeling
* Moves markdown cheatsheet to the edit modal, for quick reference