Revert "Remove mongoose, mocha-mongoose"

This reverts commit a9688b4560b352197b5acf551b29124708ef1c17.

Removing mongoose and company was a little hasty; I still need to
migrate user data from mongodb to the relational DB.
Revert "Remove old mongoose models"

This reverts commit 29d6e7b6f6b1699df91d37584135b93716341ee2.

Removing the old models was a little hasty; I still need to migrate user
data from mongodb to the relational DB.