Enables LMS to handle deprecated URLs

LMS-2651
Also note that we do import from one settings file to another, so you may want to define them all in one place (probably lms/envs/common) and import them here.

See eg https://github.com/edx/edx-platform/blob/master/cms/envs/common.py#L32 and https://github.com/edx/edx-platform/blob/master/cms/envs/common.py#L298