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.
This is a clone (copy) of CSMH's declaration and methods with an added
id of UnsignedBigInAutoField
We should be able to delete the save_history code, but needs testing.
Add error logging when capa failures happen
Put StudentModuleHistory into its own database
Bump out the primary key on CSMHE
This gives us a gap to backfill as needed.
Since the new table's pk is an unsigned bigint, even for people who don't
consolidate CSMH into CSMHE, the lost rows are unlikely to matter.
Remove StudentModuleHistory cleaner
