Create a calendar event library

As I was developing the Spring 2025 academic calendar, I realized that not all parts of term use the same events. Of course there are those that are required like the refund dates and start date and last day of exams, but not all require holidays, study days, or last day to resolve incompletes.

To make this easier in the future, I propose the creation of a calendar event library that collects all events, indicates whether they are required, and the parts of term that use them.