Add HTTP basic auth

[david4096]

So that a username/password combination can be provided by environment variables to the service. All endpoints (except service info?) should be under auth.

Close with tests that demonstrate the server running under basic auth using a client that can use the username/pass combination.

For examples of making pluggable auth with connexion see dos_connect:

https://github.com/ohsu-comp-bio/dos_connect/blob/master/dos_connect/server/basic_authorizer.py