Added basic user authentication for issue #17.
Implemented basic authentication for issue #17.
Finished implementing authentication and user management to close #17.
Added features to make deployment of the authentication features easier.

1. If there are no users in the db, the users/add route becomes public.
2. It is no longer possible to delete the last user.
Merge branch 'authentication'

Conflicts:
	flex2sms_schema.sql