Add user/password alternate login method

[rlmv]

There have been a few times when it would have been useful for users who do not have active Dartmouth accounts to log into the app. For example, exchange students who had not been assigned a NetId yet, or Kassie Amann who was interested in doing some research over past incident reports. I will also lose access to the app after my NetId expires - it might be useful for me to maintain access to the app.

This would require adding a different login route using username/password.