Issue #1318 New account size and spacing tweaks

Made option to create a new account more obvious.
Spacing
Added system for optional apps to modify settings
Fix confirmation dialog when exiting editor (#1756)
Serve static media directories correctly (#1757)

Before we were only serving staticfiles from the first app that had a
static/ directory.  For some reason we also serve admin static files,
which I still don't understand.  However, any other app static
directories would not work.

This change makes it so we serve files from all static directories.
Fix VideoUrl.get_type_display (#1760)
Support for custom CSS in editor
Changed background color of header of editor
Merge pull request #1761 from pculture/gh-1760

Fix VideoUrl.get_type_display (#1760)
Merge pull request #1738 from Lynxfive/staging

Issue #1318 New account Size and Spacing
Merge pull request #1758 from pculture/optionalappsettings

Added system for optional apps to modify settings
Merge pull request #1759 from pculture/gh-1756

Fix confirmation dialog when exiting editor (#1756)
20px was too big for the links, made it 16.
Do not show ref subtitles menu if there is no ref subtitles
Parametrize button to switch to legacy editor
Merge branch 'staging' into gh-1766
bump up commit for unisubs-integration
Merge pull request #1770 from pculture/gh-1769

bump up commit for unisubs-integration
Merge pull request #1771 from pculture/gh-1765

Gh 1765
Merge pull request #1772 from pculture/gh-1766

Gh 1766