Now possible to prohibit a Collection of Actions from being included in the List of returned actions (or as a single returned value).
All unit tests now pass with the exception of MonteCarloUCT.
TODO: playerToMove and previousPlayerPassed should be made part of the GameState.
This would remove the superfluous Player parameter from many methods and make it possible
to check for the "I'm ahead and my opponent is offering to end the game" killer move.
Player and Action classes are now singletons (factory pattern) rather than String values.
Implementing more general treesearch code for minimax, alpha-beta, monte carlo using simplified backup logic.
Removed unnecessary distinction between policy and tree search (tree search is a special kind of policy).
Calculation of all valid moves / arbitrary sets of moves is now a seperate class, as it serves a different purpose than a policy.
Introduced regression error in AlphaBeta test.
