refactor:

+added bold font to the name of the subject in json to excel converter +added new keyword in excel parser. Now "Doen't have the course" excludes the group from the list of lecture groups, and "Not needed" simply skips adding the lab to the list of classes. With that feature, new functionality added: now there may be a courses that have only lectures, and moreover, those lectures may be dedicated to the specific groups

Closes #26 (closed)