Deprecated edx-platform import paths
(for example, `student` instead of
`common.djangoapps.student`) currently raise
warnings when used. We want to fully remove
support for those paths.

As an easily reversible way to initially remove
support, we add a new setting to LMS and Studio
called `ERROR_ON_DEPRECATED_EDX_PLATFORM_IMPORTS`,
defaulting to False. We set it to True for devstack
and will set it to True in Stage and Production
soon. If critical errors occur, we can easily
flip the setting back to False.