Refactor !SasView Category code

[butler]

Once we move to adding default categories to the python model we will need to change the SasView category code to take advantage of it. Mainly:
1) Remove default.json from the repo
2) Change the code to create a serialized.json from model information instead of looking for default.json
3) If model is not in serialized.json, first look in model information for default categories. If none then, and only then, add to uncategorized.