Disallow deleting people who own projects.
Sort the graphviz input for deterministic digraphs.
Add per-project graphs

Show a graph with the project of interest at the centre of single depth to
parents and children.

Also use the correct URL for the graph, instead of hard-coding it.
Use default model constructor and keyword args.
Use singular table names for sanity.
Make Projects have many contributors, instead of one owner.
Add object names to page titles.