New feature: Rename scans
I added renamescans.sh. Guided by the grading info sheet, scans, usually (when scanned by Triumph Adler machines which are quite common in RWTH institutes) named something like ScanYYYYMMDDhhmmss.pdf, are renamed to the exam-scan file-name convention. It is assumed that the person who scanned the exams scans them according to the ordering in the CSV file.