[SOL-1864] Hide code field for quantity > 1 coupons

WL-434: Support theme previews via URL parameter

Fix for new offer landing page.

Check for enrollment API response

[WIP] [SOL-1847] Change not-selected values to null on toggling catalog type.

Fix voucher offers API endpoint

[SOL-1845] Check if user is enrolled on coupon redemption

Before redeeming a coupon and enrolling a user check if the user is already enrolled in that course.

[SOL-1819] Multi offer coupon.

Enable ONCE_PER_CUSTOMER and MULTI_USE coupon types to have max_uses and quantity > 1 at the same time.
This requires each of the vouchers to have individual offers associated with them.

Added ellipsis to long offer page course title

[SOL-1831] Show maximum uses in coupon detail page

Seat Types formated, tests added

Fix voucher offers API endpoint

Cache voucher offers

Bump up page_size when calling course catalog

Use the correct error template

[SOL-1785] Frontend changes for new invoice fields.

[SOL-1629] Added multi courses landing page

Refactoring code

Error handling when course info not available

Tests for multi course landing page added

Code refactoring

Catalog query added

Backend refactored

Layout

Lots of changes

Added digg pagination

Tests

Coupon redeem view test updates.

Logic into backbone

Tests added

Pagination added

Fixed certificate bug. Comments addressed

Jasmine tests written for pagination

Python tests fixed

Comments addressed, small visual changes

Comments addressed, error message template

Enroll now, comments addressed

[SOL-1785] Backend side for new invoice fields.

[SOL-1825] Refactor coupon redeem view to API

Admin updates

We don't use this field, and we have so many users that the page times out.

ECOM-4725

ECOM-4725

mattdrayer/WL-530: Allow Enrollment Code purchases for enrolled users