USE_MMDB_ID

Changes comments3 to use the MMDB User id while building the JWT token that is passed to livefyre.

To test this you can checkout branch "ngm_745" of project NGM and branch "use_mmdb_id" from django-comments3 and when you click the user avatar or username, it should bring you to the user's membercenter page with their vanity url.

e.g. http://membercenter(-environ).nationalgeographic.com/vanity_url (e.g. /12345678)

Jira:
https://ngjira.nationalgeographic.com/browse/ngm-745