Improve Model.toString()

[petebankhead]

No description provided.

[alanocallaghan]

If I'm parsing this right, it means the toString changes from just model name to [parentdir]/[name]-[version], leaving out parentdir or version if null? lgtm, although will conflict with #76

[alanocallaghan]

Ah, no, insert the directory name if it's not the model, I see

[petebankhead]

You didn't really have to merge this if it doesn't fit with the versioning plans :)

But yeah, the name stored within rdf.yaml might not match the directory name, and so there would be subtle clashes causing models to be dropped due to names not being unique... despite looking unique in the directory.

Also, it's not obvious to the user that the name in rdf.yaml is being used - and so they might rename the model directory and hope that is sufficient.... but it is not.