Add option to rejudge latest submissions

[pverscha]

trafficstars

Right now there's a filter option to rejudge only the latest correct submission for students, but I think it would be very useful if it's possible to rejudge the latest submission (regardless of it being correct or not).

[chvp]

Should probably just be done by allowing to filter for latest submissions (and then taking this filter into account when rejudging).