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.
Support for custom CSS in editor
Merge pull request #1771 from pculture/gh-1765

Gh 1765