Wrap editor content in a div

This is nice because we can use ng-cloak on this and not have to use
it for every section.  Also if we want to set a max-width, this would
probably be the element to do it on.
Editor HTML refactor

The HTML file was getting pretty huge.  Used django templating to
split it up.  This should also make it easier to refactor the layout

Tried to make the indentation consistent at 4 spaces per indent.  Now
that stuff is in different files we have more width to work with.

Lots of changed lines, but basically no changes to the HTML we render
other than whitespace changes.  The one change was to add a couple
missing </button> tags to properly close things.

Moved all the templates into the editor subdirectory.  I actually
think that we should have an editor app eventually and move the code
out of the subtitles app.
Removed collab stuff from the editor

We had a bunch of code here but little functionality.  The only thing
it provided was notes and task approval.  I'm going to be reworking
both of those as part of some other tickets, so I figure the simplest
thing to do is just rip it out and rebuild from scratch.
CSS refactor

This change changes the SCSS so that the CSS for page elements like
div.subtitles-wrapper, aren't nested inside their container
(section.center in that case).
Reworked editor layout

Changed basically everything to use absolute positioning.  I think
this is the most logic way to do things because we want the content to
fit exactly on the page.  It also makes it simpler to move things
around and fixes the bug I was seeing when I changed my zoom size.
Merge pull request #1668 from pculture/editor-changes

Editor changes