Add cTree test user list

[CSchmitz81]

• add test users as add test elements (randomly reuse existing user or introduce new test user)
• populate with random name, thumbnail, & other appropriate values from Lorem.html
• users should be per cTree (we'll add a concept of global users linked to cTree users later)
• keep track of what's assigned to user for user history

[CSchmitz81]

To add a bit more background, we currently populate the designer, contributor, and reviewer fields with just strings (all marked with "TODO: should probably be an object" in a comment in ctree-loader-behavior-test.html). These should be updated to hold a reference to a user object (the structure is documented in the same comment as the TODOs). All users for a test cTree should be stored under "users" in the test cTreeData. As elements are created you should randomly decide to create a new user or use one from the existing users list (probably equally weighted). The existing places where the user strings are used will need to be updated to get the name from the user object.