Updates to Demographics Display

- Gating on feature enabled for Open edX users
- If feature disabled and Insights URL is set, displaying message pointing users to Insights
Studio: cleaning up/removing unused sass

* removing unused font-family-centric Sass variables
* removing unused graphic images and Sass references
* clean up of style removal fallout
deleting more things
Remove extra large-FOO-icon.png files
Removed more files from cms
Deleted some unused images under common
content-types is no longer around
re-add search-icon.png
Remove "ADMIN_MEDIA_PREFIX" (deprecated in Django 1.4)

Delete lms/static/admin resources as they are no longer needed
for the admin page as of Django 1.4

Moved two files that were referenced elsewhere:
lms/static/admin/js/jquery.min.js -> lms/static/js/admin/jquery.min.js
lms/static/admin/js/urlify.js -> lms/static/js/admin/urlify.js
fix click event for actual target
TNL-138
Merge pull request #5782 from edx/remove-analytics-demographics

Updates to Demographics Display
Merge pull request #5808 from edx/zub/bugfix/tnl-138-createunitthrowserror

fix click event for actual target
Merge pull request #4806 from edx/talbs/studio-stylesweep-unused

Studio: Removing older/deprecated style rules
Implement shim for mobile video events.

This PR addresses the following issues:

1) All requests return a 200 OK unless there is an authorization failure. This is deliberate in case the secret key is compromised.
2) Push all of the nasty logic necessary to generate compatible video events into the LMS instead of trying to do that mapping on the mobile devices.
3) Stop using the deprecated "action" field in the segment.io event. According to their support team this field should not be used anymore and is just around for backwards compatibility reasons.

Fixes: AN-3818
Abstract asset methods into own interface class
then impl the read ones as NotImplementedError placeholders on xml modulestore
PLAT-70
fixup! Remove "ADMIN_MEDIA_PREFIX" (deprecated in Django 1.4)
Merge pull request #5781 from mulby/mobile-eventing-v2

Implement shim for mobile video events.
Remove more pep8 violations
Merge pull request #5828 from edx/sarina/moar-pep8

Remove more pep8 violations
Merge pull request #5800 from edx/dhm/xml_assetstore

Abstract asset methods into own interface class