all dirs must now go into COMPREHENSIVE_THEME_DIRS.
Move comprehensive theming setup section out of startup.py and into
  settings files using new 'derived' functionality.
Add 'derive_settings' at the end of all top-level Django settings files.
Move validation of comprehensive theming settings into new apps.py
  theming file.
Split theming code into code safe to run before settings are initialized
  -and- after settings are initialized.

 The CCXCon app is used to push course updated to the CCXCon
 externale service.

Please note that this is a squshed commit and the work of:
Symbolist, macdiesel, nedbat, doctoryes, muzaffaryousaf and muhammad-ammar

The old line:

    from path import path

produced pylint errors because of the baroque way that path.py defined
"path".  We tried to get them to change how they defined it, but they
deleted the name instead: https://github.com/jaraco/path.py/issues/102

(Jason then changed his mind, but this is a better way to use path.py,
it avoids the pylint error at least.)

This makes these files importable, and puts them into the new best guess
as to where files should live.

This reads configuration directly from yaml
and imports it directly into settings