Add matrix uuid to evaluations tables [Resolves #591]

[thcrock]

• Add matrix uuid column to both train and test evaluations table
  schemas,
  updating the factory as well and adding migration to create it
• commit session in test util MockMatrixStore so the matrix actually
  shows up in the database
• In ModelEvaluator, include matrix_uuid in evaluation data sent to
  database

[nanounanue]

I would recommend to name this column as test_matrix_uuid instead of just matrix_uuid

[thcrock]

The problem is that the evaluator works on both the train and test evaluations tables. I added the column to both because I figured unless there's a good reason we should keep the schema of the two tables as similar as possible. matrix_uuid works no matter which table it is. Options:

1. Actually neglect to add any matrix column to the train evaluations table (you could get it by joining to models)
2. Add the column to both tables, but prepend train or test to the column name in each one
3. Add the column to both tables, with a generic name that works for both.

What do you think?

[nanounanue]

I think that, for the moment, option 3 is the best.