Minor additions, added comments, few changes in use of data structures.

- Attempted to write the "CRUDUser" methods. Didn't get very far, since we don't have a DB to interface with yet.

- Looked through existing code and comments. Made minor cosmetic changes and answered some questions in the comments.

- Changed the used data structures a few places.
A standard List was being used. The intention was clearly for the List to only contain unique elements. I therefore changed it to a HashSet, saving us from having to check for List membership ourselves. :-)