Filtering by feedback option should switch grader filter away from ungraded
The default grader filter is ungraded. This results in a confusing behavior when the user selects a FO filter and there are suddenly 0 solutions available (because all solutions with FOs selected happen to be graded).
While it is possible that a solution was set aside, and matches the filter, we should still base the UI on the most common use case. Therefore I propose that whenever the user changes the FO search filter to nonempty, and the grader filter is at "ungraded", the grader filter should switch to "all".
Note, however, that changing the grader filter to "ungraded" shouldn't empty the FO filter, since this would allow to search through the solutions that were pregraded or set aside.