ShortDeckPokerState needs .is_chance @property

[fedden]

As mentioned by @big-c-note we need to introduce the is_chance property to the state class to allow us to use the complete unadulterated blueprint algorithm.

https://github.com/fedden/pluribus-poker-AI/pull/40#discussion_r402033698

[fedden]

We'll need to move the logic that deals cards to be done at the right points, and update what actions should be made at a chance state (if any at all). If no actions are made, then what does that interface look like?

[big-c-note]

The "action" can be dealing. Chance nodes only happen during dealing, so the action can be dealing, and we can apply the action ('flop deal', 'preflop deal', etc) to the state class.

Attribute is_chance can be updated to False, so we will not execute that conditional again in the recursion until the game state reverts is_chance back to True, signaling that we have completed the betting round

This also makes the algorithm more application independent