Revised models/__init__, /importing, and /analyzing

- Commented the Model class in __init__
- Improved comments in analyzing and importing
Wrote Tests for models.importing.Importer.insertRows()
Wrote Tests for models.analyzing.ListOfPieces
Unit Tests Now Run

- Wrote an __init__ file for the models_tests module.
- Wrote a run_tests.py file that runs the unit tests.
More Removal of VisSignals()

We may eventually use our own signals-and-slots implementation,
but not today.