Add a default Workflow model.

This essentially moves the Workflow model from the test app into the Taverna
Player namespace. It should make setting things up from scratch a lot easier and
can still be overridden with a custom Workflow model.
Fix up the user proxy for tests vs the dev app.

The tests should use the fixtures, the dev app should use a defined user.
Update the installer templates.

Now refer to the Taverna Player Workflow model.