Create quasi-thrifty/quasi-greedy selection methods for SETGame class

[mitchellfaulk]

Adapt the algorithms from the setgametools.py script to create a method for the SETGame class which selects SETs via the quasi-thrifty or quasi-greedy algorithms.

[mitchellfaulk]

@l-rettberg if you want some practice with Python classes (and the card game SET and using GitHub)