Use a template function to sort alums

[rachitnigam]

The current alum sorting logic is a bit weird and relies on an unnecessary sort field which defines the degree with which an alum graduated. There, the order in the file determines how people are printed out on the webpage and is currently sorted by year.

A better solution would be to use a custom function which is passed into the template and used directly. That way, we could get rid of the sort field and automatically sort by degree & year.