Implement login/auth APIs

[hattifnatt4r]

For the first project, I'd like to get help from experienced developers with login/auth APIs so we don't get stuck on this stage.

[rlivings39]

Working on this now. I'm doing the work in this branch

https://github.com/cambridge-devclass/ambient-app--react/tree/ryan-server-setup

[rlivings39]

After PR #26 I think the last step would be to add a few tests to ensure things work properly. I can take a look at that next week.

That will also give people a scaffolding for writing their own backend tests.

[rlivings39]

Last step is to revisit how we pull in the DB config. See the review comments in #27 for more info.