Use a Student class to provide calculated properties

[ryansb]

There are a few places now where we execute some logic and add properties to students. It'd be better if we could do something like this.

class Student(object):
    @property
    def participant_page(self):
        return "/blogs/{year}/{term}/{uname}".format(......)

This will require a fair amount of changes to existing code, so before doing this we should work on decause/hflossk#419

migrated from decause/hflossk#420