Implement greedy cohesive rule and greedy justified candidate rule

[martinlackner]

Add the Greedy Cohesive Rule (and perhaps variations of it), as well as the greedy justified candidate rule of Markus Brill and Jannik Peters (suggestion from @DominikPeters )

[erelsgl]

What is a reference for the Greedy Cohesive Rule and some interesting variations of it?
What other algorithms from that paper are worth adding?

[martinlackner]

I looked at the paper again and I think the Greedy Cohesive Rule is actually the only one really relevant for abcvoting. So that's a very simple task.

[erelsgl]

What is a reference for Greedy Cohesive Rule? I did not find it in Brill & Peters' paper.
Also, the Brill & Peters' paper also contains algorithms for checking properties such as EJR+. Are these algorithms relevant for abcvoting?

[DominikPeters]

The Greedy Cohesive Rule is defined in https://arxiv.org/abs/2008.13276. However, I recently noticed there is an error in the definition, it should say $T \subseteq C$ instead of $T \subseteq C \setminus W$ (otherwise the proof that GCR satisfies FJR fails), and this has not been corrected yet. It's probably prudent to start with GJCR since it is more practical

[martinlackner]

Properties are definitely interesting, although EJR+ is already implemented. See also #96 , which is related