Implemented notes in the editor

Added editor code and tests to display notes.

The backend code is not implemented yet, we just send fake data at
this point.

Added username to editor_data.
Added backend code for subtitle notes for the editor

Updated sphinx conf.py to run startup().  This sets up the python
python just it is when running the app.
Implemented adding notes

Added API endpoint to add notes.  Updated editor javascript to POST to
the API.

Fixed API authentication.  Now we correctly require that a user is
logged in to view our API endpoints.
Editor UI updates for notes.

Made the timeline a bit darker, it was looking weird when it had the
same background as the review and notes section.

Hide the sync helpers when not playing video.  They cover up the notes
section, which could be weird.

Fix for positionSyncHelpers to keep storing the position even if the
sync helpers are not shown.
Implemented team editor notes

Made a abstract base class for SubtitleNote.  This makes it easier to
have alter the notes section.  Used it to create TeamSubtitleNote.

Made all team videos result use a TeamWorkflow object.  This makes the
team notes work.  I also think it fixes some permissions issues for
private teams that don't use tasks.

Made editor correctly display the heading from our workflow in the
notes section.  Fixed clicking the add note button so it doesn't add
"#" to the URL.
Use django-rest-framework's APIClient instead of a homebrew.
Fixed gettext call
Added space between notes list and heading (#1709)
Fix for linebreaks in editor notes (#1708)

Also escaped other HTML from the notes.
Editor style updates (#1707)

- Don't show the video overlay in review mode.
- Wording changes for review mode.
- Fixed text position on review buttons.
- Changed note textbox to a light background.
- Shortened notes heading
- Fixed border at the bottom of the video controls that didn't match
  the rest of the layout.
- added text that notes are only visible in the editor.
Add back icon for the tasks lisk (#1703)
Have team videos inherit from DefaultWorkflow (#1714)
Send emails when notes get added to task teams (#1470)
Fixed margins for the notes section (#1713)

Added margin to the notes list.  Made the side margins for the heading
match the ones for the notes.  Made it so the first note doesn't have
a top margin (and similarly for the last).
Fix posting notes to task teams
Send messages as well as emails for team notes
Better text for messages
grammar police
Merge pull request #1717 from pculture/editor-notes

Editor notes