FIX Allow FALSE in Config API, call remove() will NULL key on update()
FIX Clean cache on Config->remove()
Formatting and docs changes to configuration.md
Disable RequestHandler->handleAction() deprecation until we have fixed LeftAndMain usage
Allow for short versions in Deprecation::notification_version()
API Marked statics private, use Config API instead (#8317)

See "Static configuration properties are now immutable, you must use Config API." in the 3.1 change log for details.