Refactor MixedBehaviorProfile caching (#703)

* Refactor MixedBehaviorProfile caching

This re-writes the cached quantity calculations for MixedBehaviorProfile:

* Uses the preorder and postorder traversal of nodes provided by the game class;
* Thereby avoids recursion to descend the tree
* Cleanly separates the computation of each vector of quantities (which will be a help for
  further optimisation in future when we look at the data structures
  used to represent them)
* Because there is a dependency order in the cached quantities,
  implements a slightly more sophisticated cache to compute
  only what is truly needed.

Author: tturocy