Fixed adding users to projects with no users

[aaroncohen73]

fixes issue #132

Changes in this PR.

• Fixed a bug that was caused by directly accessing dictionary items instead of using setdefault

Testing this PR.

1. Run flake8 app testing
2. Run nosetests
3. Sign in to the timesync-staging server and run cp to create a project, but don't add any users
4. Run upu and add a user to the project (note: the user might not show up in the output of upu)
5. Run gp to get the list of projects and see that the new user was added to the project

@osuosl/devs