LDEV-5272 Allow deallocating answers from VSA options
Also fix a bug: when a teacher allocates an answer, the learner's
question result UID was used. If the learner changed his/her answer
before teacher allocated it or refreshed the page, the new answer got
allocated while the teacher thought the old one was getting allocated.
Now all allocation happens based on real answer value.
Also recalculate scores on allocation even if a learner has not finished
the activity yet.