Corrected the way the test code is structured.

- Use defaultBases rather than subclassing.
- Ordered the setup bases correctly.
- Use the minimum possible classes.
Add a new URI loader for PMR

- Generates own URI scheme for use with internal items.
- Very barebone at the moment, will need more tests.
- It will have to allow relative linkage of all kinds that have been
  implemented but a few are likely to work incorrectly.  However the
  baseline test currently passes.