ECOM-1808

Resolve merge conflicts

Fix: users without course creation permission were not shown new libr…

Conflicts:
	requirements/edx/github.txt

update xblock only to mark field values as dirty if they've changed (…

force save "download_video" field if not set

set timezone to UTC explicitly

Fix login/logout errors caused by unicode cookie names

Update translations (autogenerated message)

Set Courseware Search to False in default devstack, because it doesn't work.

Make header & footer responsive

Fix SEARCH_ENGINE set logic in settings files

Update i18n-tools to latest version LOC-67

Feature: Shibboleth/SAML SSO

[LTI Provider] Added an authentication backend to log in LTI users

Clean up capa polling to have exponential backoff

Making background pictures printable

fix the source_version xblock after discard changes

Fix dark lang and django.middleware.locale behaviors 

Adds a temporary user_preference key, DARK_LANGUAGE_KEY, to hold the user's dark lang preference.
This preference key is deleted when ?clear-lang is placed in query params.

This change adds a Django authentication backend which, when installed
will authenticate users based on their LTI identity rather than using
a username/password combination. The authentication method determines
first whether a user with the given username exists and, if so, whether
that user is associated with an LTI identity. It also verifies that
the LTI consumer and user ID passed to the LTI launch match those
stored in the LtiUser table. This will always be the case if the
authentication backend is reached through the LTI code, but it
provides an extra guarantee if the backend is called from elsewhere.

Tests would have caught issues raised in LOC-87

LOC-87