JLFP: Task-aware wss overhead charges (pythonic)

This is a pythonic approach for task-aware wss overhead charges, unlike my prior patch on the "prop/task-aware-wss" branch. It's O(n lg n) instead of O(n), but it is much more pythonic.  I will explore a native implementation for overhead charging, where efficiency can be addressed more effectively.

(commit description)
The JLFP overhead model currently charges the same max-wss CPMD
to all tasks of a task set, even if each task has a different
wss. Instead, each task should be charged the max-wss CPMD, except
for the task with the largest wss. This task should be charged
a CPMD for the second-greatest wss.