2. Add site configuration overrides to theming/helpers.py
3. Move microsite.get_value from theming/helpers to site_configuration/helpers
4. Move microsite_configuration.microsite.get_value usages to site_configuration.helpers.values
2. Update COMPREHNSIVE_THEME_DIR to COMPREHENSIVE_THEME_DIRS
3. Update paver commands to support multi theme dirs
4. Updating template loaders
5. Add ENABLE_COMPREHENSIVE_THEMING flag to enable or disable theming via settings
6. Update tests
7. Add backward compatibility for COMPREHEHNSIVE_THEME_DIR
* mattdrayer: Add helpers.get_value test
* mattdrayer: Change to simpler implementation, per @douglashall
* mattdrayer: Address quality violations and test failures