add expected value to feedback-type

[KBorm]

I would like to have something in the subtest results that can respresent the expected value versus the submitted code output in order to generate a table in LMS:

input description | extected | got
-----------------------------------------
18                | 6        | 7
12                | 10       | 10
25                | 10       | 10

• input value description (minOccurs = 0, type=html/plaintext)
• expected value (minOccurs = 0, type=xs:string)
• output value (minOccurs = 0, type=xs:string)

could be added to the feedback-type

[upriss]

Same comment as for Issue #6: maybe we need a test-type specific namespace because this is only relevant for unit tests