Store replayed results

[GuillaumeDerval]

In an not-so-orthogonal way to #618, we could store previous gradings for submissions, allowing to restore previous gradings if needed when something went wrong while replaying.

[GuillaumeDerval]

This is complimentary with #618: a rejudging could be a stored replay not applied by default (i.e. that is not the "selected grading among all the gradings done on this submission")