Changed email to username in the request body of the /login POST handler.
Added some error checking for a badly constructed 'auth' object in configuration.
The names for the auth collections that store users and tokens can now be specified in the auth configuration object.
Updated example auth configuration.
Converted over to using MongoDB connection string to connect to the main database. This allows use of the simplified MongoDB connection API.
The explicit calls to authenticate with MongoDB have been removed although this should still be possible via the connection string.
Simplified the integration tests.