Reorganise reindexing operation

An upgrade to verified should emit a mode_changed event.

This change will also move us to bok-choy instead of lettuce for
these scenarios, and re-enable them. See TE-736.

Includes some refactoring of repeated event-checking code as well.

Disabled flaky JS tests pending refactor to Backbone

Placeholder text for <iframe> encourages inaccessible content

Fix embargo migration to the new data models.

The previous version of this migration incorrectly handled
disabled configuration.  When configuration is disabled,
the embargoed country field was the empty string; calling
str.split(",") produced a list with a single empty list entry,
which is not a valid country code.

Vote buttons should be disabled while in use

Add InvoiceHistory model to record changes to invoices

Fixed ajax login when advanced security check is on for NoneType user.

Release

TNL-1352

Enable split for new courses.

Iframe unit in the studio have accesibility issue as there was no title for
Iframe provided as well as placeholder does not specify what changes to made
to add new iframe

TNL-1073

ECOM-1045: Add messaging for when students miss the verification deadline

xml_importer now calls store.has_course even if create_course_if_not_present is False.

TNL-1362

Split modulestore throws duplicate errors if course locator is not unique.

With split, "name" returns "course" instead of the run name.

Don't instantiate bogus modulestores just to get template rendering in o...

Aamir khan/ecom 996 country access settings

Testing migration from old mongo to split.

Tests verify operation counts for old mongo. Should be extended to split in the future.

Cannot create an xblock in a course that doesn't exist.

make_asset_key does not start with "/" for split locators.

"run" should not be passed in kwargs to create.

Cannot hold on to xblock references.

Have not been able to work out why.

Get updated xblocks from modulestore before checking properties.

Note that now 2 courses can be imported where the only difference between them is run.