added another project to which the project_user is a member
added the project_membership between project_user and project :three
added a project_affiliated_record created by :project_user affiliated
  with project :three
test/models/project_test tests that a project_user can update
  project to which they are a member, like core_users
test/models/project_affiliated_records tests that project_users
  can create and destroy project_affiliated_records between their
  records and projects to which they are a member
models/ability.rb makes it so that these pass
test/controllers/projects_controller tests that a project_user
can affiliate single and multiple records with a project if they
are a member, just like the core_user
ALL TESTS PASS
tests that project_users cannot manage project_memberships even if tey are a member of a project. ALL TESTS PASS