Create web users, create projects, and assign users to projects

[yanokwa]

I wrote a provisioning script to create web users, projects, and assign users to projects. I had to use the REST API and I think it'd be nice to have pyODK have. And to be explicit, I don't think there should be a method that does this in one go. I'm arguing for methods to do each of these individually.

I haven't thought at all about what they pyODK methods would be called and what they'd be associated with. Some are pretty obvious (e.g.,projects.create(project_name, project_description)) but where users and assignment are require some thinking.