Additional currentTurn test added

* Player needs to wait current turn on enterPawn
* DRY-ed up some code on parcheesi.js
* Added index property to pawn entity
Added a couple of tests on pawn.js

* Added a couple of comments on parcheesi.js explaining rules
* Added rules to prevent users from making moves not present on the dice, or making
* Added new empty tests on gameplay.js
* Added new method on utils to detect available moves, instead of using _.difference