Add back link to player restriction

This demos the process of how to add the back links from the "restricted game" player object to the corresponding object in the unrestricted version.

It also tidies up some formatting -- in particular, always use two spaces for each level of indentation, and never tabs.

What's next: add and populate similar back links in the game representation, and each GameStrategyRep in the restricted game, following the pattern here.  There's not a need to worry about GameOutcomeRep (for reasons we can talk about at some later point).