Refactored Evaluations page

- UI has been slightly refactored, more work is needed
- due to the refactoring, the answer author api function has been
removed (including its tests)
- removed answerpair api functions. Currently it is an empty model.
I've left it to create other api functions required for reports for
example.
- created an api function to return all of the students in the class
and its tests
- removed duplicate dataformat for CriteriaAndCourses
- refactored "notScoredEnd" filter to not use Javascript's filter
function
- created a function to query for the evaluations' answer pairs
when called from a link. This is so that we do not load all of the
data initially or else it may increase the loading time for
unnecessary data
added error message for duplicate usernames in class import file

- I have also moved the errors to the top of the page, so that they
would not be buried under all of the successes