Add the concept of a "category" to each student, and separate groups based on categories

This is a request to add the concept of a category. It can be anything, and it can have any number of options.

For example, a category for first language:

• English
• Spanish

Each student in the caseload would choose one item from the category. The scheduler would keep students having different categories separated.

This is related to the following other feature requests:

• Specify preferred groups
• Bilingual students