Enforce a rule preventing self-reviews

[MichaelNMaggs]

Would like added functionality (probably set 'on' by default) to ensure that a juror is never presented with their own images for review.

Montage already has a 'disqualify jurors' setting, which is needed to avoid conflicts of interest in cases where the jurors/reviewers are going to take the final decisions. In the UK, though, we distinguish between 'reviewers' whose task it is to help us cut down the numbers and our panel of (generally professional photographer) 'judges' who will make the final decisions in a face to face meeting. As we have large numbers of entries (over 14,000 this year) we need all the reviewers we can get, and we can't afford to disqualify reviewer submissions or we'd make it even more difficult to get volunteers! There's no conflict in a reviewer having images in the contest provided that he or she is not asked to review their own submissions.

We're fudging the issue manually this year, but it would be good to have this functionality in place next time.