Fix watcher and add gray background for unscanned exams
Fix watcher and add gray background for unscanned exams

* The watcher was giving redundant messages because of
the way the scanner writes the results. It was thus
uselessly reloading the files over and over again.
A timer was introduced to avoid reloading the results
so frequently.

* Unscanned exams are now also shown, but in gray.

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