Ignore dot files when loading users

This allows other files and folders to be in the users directory, e.g.
.git. They must be named with a dot in the front.
Revert "Add downloading of grades to excel file"

This reverts commit 8d4130e5fa123d2c156b42bdf44b097594c84f22.
Add an optional comments field for grades

Append a tab and then the comment in the user files

example:

grade lab01	8	10	forgot to do part 2