Add partner scoring to ok client

Staff can specify Tests that are specific to a particular partner by adding a 'partner' field to the tests:

    test = {
        ...
        'partner': 'A',
        ...
    }

The partner string can be any arbitrary string -- it is up to the staff to be consistent. If the 'partner' field is omitted, the test will apply to all partners. The actual field will be assigned a value of `core.Test.DEFAULT_PARTNER`, which is assigned to the empty string (but can be changed).

Here is an example of the point breakdown:

    Partner A score:
    24.0
    Partner B score:
    24.0