`tree.py` bugs & improvements

[beckyjackson]

• Parent terms all have the same href as the target term, so you cannot click back up them
• Terms with no label will cause the script to fail
• We should allow a default with no term arg that just shows the top-level under owl:Thing

[beckyjackson]

Also, should we add the db param as part of the query string? If we don't, we potentially need multiple tree.sh scripts for each ontology we want to browse.

[jamesaoverton]

Yeah, that sounds right.

[beckyjackson]

I'm going to wait for #18 to be merged until working on this to prevent any weird conflicts.