Refactor ADVANCED_COMPONENT_TYPES

    Modified to a setting in CMS common.py and aws.py
    Also factored out are: ADVANCED_PROBLEM_TYPES

    This enables third parties to add XBlocks to their system
    without having to make a code change.

    Code also added to ensure that a component should exist in both
    ADVANCED_COMPONENT_TYPES and the course advanced module list
    in order for it to be enabled in the course.
Added clarification for events that do/not include session values
Merge pull request #4683 from edx/ahodges/documentation/AN2976

Added clarification for events that do/not include session values
Merge pull request #4512 from Stanford-Online/dcadams/refactor_advanced_component_types

Refactor ADVANCED_COMPONENT_TYPES
Fix filter with new opaque key, allowing user to set COURSE_LISTING as old way path
Cleaned pylint quality issues in instructor email content history code.
Merge pull request #4688 from Stanford-Online/njdupoux/email-content-history-qualityfixes

Cleaned pylint quality issues in instructor email content history code
Fix Video Player Initialisation Issue
Merge pull request #4691 from edx/ammar/fix-video-init-issue

Fix Video Player Initialization Issue
Merge pull request #4254 from marcore/fix-branding-course-listing-opaque

Fix filter with new opaque key, allowing user to set COURSE_LISTING as o...
TinyMCE Plugin: Added media plugin to TinyMCE for the Annotation tool

- fixed missing media and link buttons on image

 - fixed a CSS issue with the sharing button