Game engine updates.

Although the visuals are not currently rendering this update includes numerous worthwhile updates to the game engine including:
* structure.json is now structure.js. This makes much more sense as it's not json it's javascript. We still use it to define game data. This allowed the removal of the eval statement
* The init method for scenes no longer passes a reference to itself. The 'this' keyword is used instead
* The safeScene class is much cleaner in it's implementation