ImageExplorer MVP implementation & fix under https

update hotspot reveal styling

address some PR feedback. Start to build out some Jasmine tests

address PR comments

add some default content

fix when running under https
capa-mrq: Added hinting/feedback mechanism for multiple choice problem type

- Added hinting/feedback mechanism for multiple choice problem type
- fix styles to make feedback act as an overlay as opposed to a side-by-side block
Add some optional policies around password resets, such as password reuse, forced password resets, allowed frequency of password resets
make GA account code configurable as well as allow GA to appear on courseware. Also, make the GA account ID configurable rather than hard coded in the Mako template

Conflicts:
	lms/envs/aws.py
	lms/envs/common.py
freetext-mrq: Add fork of the mentoring XBlock repository
image-explorer: add reference to image-explorer
drag-drop: add MVP implementation of drag-and-drop xBlock
Enforce type of the XBlocks Fields when set

This updates the XBlock dependency to edX/XBlock@cba8d788f0c16802b4cc468ccb6dc765b62e55e8
and add the newly introduced enforce_type methods
mentoring: Update commit hash (MCQ, MRQ & Free Text Answer changes)
mentoring: Update hash
xblock-external-ui: Add XBlock API call to render XBlock views

Included commits:
* xblock-external-ui: Include CSRF token in the API answer
* xblock-external-ui: Adds support for CORS headers (cross-domain request)
* xblock-external-ui: Include full path when building local_url
Merge pull request #6 from edx-solutions/xblock-external-ui-solutions

Xblock external UI - Server-side integration
mentoring: Update commit hash
Initial API implementation