Add fuclean script

This script deletes all the empty directories of students who have not
submitted anything (for example because their practice partners
submitted the assignment). Excluding those on the whiteboard web
interface does not help here, since then they are not part of the grade
table.

fuclean.sh

+#! /bin/sh
+
+if [ ! -f 'grades.csv' ] && [ ! -f 'grades.xls' ]; then
+    printf "Execute within the directory containing 'grades.csv'\n" >&2
+    exit 1
+fi
+
+# Delete empty comments.txts so we can more easily delete empty directories.
+# Otherwise they would still contain this one empty file.
+find . -type f -name "comments.txt" -empty -delete;
+
+# Delete all empty directories in the directory containing grades.csv
+find . -type d -empty -delete
+
+# Re-create the (now deleted) feedback attachment directories and comments.txts for the student directories that are left.
+for dir in *; do
+	if [ -d "${dir}" ]; then
+		mkdir "${dir}/Feedback Attachment(s)"
+		touch "${dir}/comments.txt"
+	fi
+done

install.sh

 #! /bin/sh
 
-scripts="fixpdf.sh fucopy.sh fufixpdf.sh fuzip.sh fuxournalexport.sh fixtimes.sh"
+scripts="fixpdf.sh fucopy.sh fufixpdf.sh fuzip.sh fuxournalexport.sh fixtimes.sh fuclean.sh"
 
 destdir="${DESTDIR:=$HOME/.local/bin}"
 mkdir -p "$destdir"