Class scheduling now explains itself when an action cannot go through.
- Restoring a cancelled class session that cannot be restored, for example because its court or equipment is now fully booked, shows a message saying why instead of appearing to do nothing.
- Saving a class that is refused for the same kind of reason now shows that exact message instead of a general "something went wrong" notice.
- Messages about fully booked equipment now display correctly in your own language, without a missing-text warning.
