creating a UUID field class
adding end-turn endpoint

Changes
* adding a common UUID field serializer
* adding a get_absolute_url function for game
* adding an end turn object for use with serialization
* adding an end turn serializer
* adding a url for end turn
* adding a name to the game view url
* adding a game common object as a helper for views
* adding an end turn view class
* adding tests for the end-turn endpoint