Game saves, performance boost, and more

- resize() is now centerAll() (works regardless of screen size settings)
- added ability to save your game (and load!)
- the methods in the Grid class use less "for loops" and create less instances
- can now get the ID of a chunk
- initial values are set upon block/tile placement and after world gen (hackish solution to a bug)
- added more debug info
- GameScreen.reset() actually resets values now