Clean up and simplify epilogue code

* Make loadEpilogueData() take, and the player attribute of created epilogue objects be, a player object reference instead of an index.

* Use .forEach(), .some(), and .every() to shorten code and avoid dereferencing undefined.

* Implement alsoPlaying and playerStartingLayers condition attributes.

* No need to figure out who won, only whether HUMAN_PLAYER won or not.

* Whitespace fixes.