When sorting achievements, make level achievements last.

Level achievements need to be processed last, and currently an
instructor can edit achievement numbers which could place some
achievements after the level achievements.

Update the sortAchievements utility method to always place level
achievements at the end of the list.

lib/WeBWorK/Utils.pm

@@ -215,15 +215,21 @@ sub sortAchievements (@achievements) {
 	# Next sort by number.
 	@achievements = sort { ($a->number || 0) <=> ($b->number || 0) } @achievements;
 
-	# Finally sort by category.
+	# Finally sort by category. Always place level achievements last.
 	@achievements = sort {
-		if ($a->number && $b->number) {
+		if ($a->{category} eq 'level' && $b->{category} eq 'level') {
+			return 0;
+		} elsif ($a->{category} eq 'level') {
+			return 1;
+		} elsif ($b->{category} eq 'level') {
+			return -1;
+		} elsif ($a->number && $b->number) {
 			return $a->number <=> $b->number;
 		} elsif ($a->{category} eq $b->{category}) {
 			return 0;
-		} elsif ($a->{category} eq 'secret' or $b->{category} eq 'level') {
+		} elsif ($a->{category} eq 'secret') {
 			return -1;
-		} elsif ($a->{category} eq 'level' or $b->{category} eq 'secret') {
+		} elsif ($b->{category} eq 'secret') {
 			return 1;
 		} else {
 			return $a->{category} cmp $b->{category};