Remove autoplay for video in course about page

The iframe was generated with autoplay=1, which, sometimes, would cause
the video to play in the background.
Add info for polls
add some rate limiting to the password reset functionality
Add change for help modal in anticipation of i18n support
Start documenting Staff Debug Info

STUD-1273
fix method name to actually make sense
Merge pull request #2711 from edx/cdodge/throttle-forgot-password

add some rate limiting to the password reset functionality
Add new container page that can display nested xblocks

This is the changes for STUD-1244, which introduces the ability for Studio to display
arbitrarily nested xblocks. In this change, a new container page is introduced which can
display nested xblocks. In particular, the xblock type of 'vertical' is special cased
to be shown inline as a collapsible section. The unit page is mostly unchanged, except
that container xblock's are shown as a link to their container page, rather than being
shown inline.
Update video docs for multiple language transcripts
Display only the first component name in the page (and nav) title.
STUD-1351
Merge pull request #2539 from edx/andya/nested-xblocks

Add new container page that can display nested xblocks
adding a little styling to the language note on the LMS help modal
Add xref to Add Files in Video docs
Merge pull request #2755 from edx/sylvia/documentation/BLD-672

Update video docs for multiple language transcripts
Merge pull request #2740 from edx/sarina/update-help-modal-language

Add change for help modal in anticipation of i18n support
Add error notification for XBlocks in Studio
Further updates to Polls
Merge remote-tracking branch 'origin/release'

Conflicts:
	cms/envs/common.py
	lms/envs/common.py
adding in gray versions of social icons for use in new email template. Using new name to ensure old links and existing emails using older templates still stay active
Merge pull request #2759 from edx/release-and-merge-conflict-resolution

Release and merge conflict resolution