Completely revamped terrain and switched y/z axis

- Rewrote Terrain.js to use binary data.
- The process for obtaining this data is documented in terrain-steps.md
- Also reworked Model.js, Terrain.js, and DefaultControl.js to switch
the y axis and the z axis so that up (vertical) is in the z axis. This
should make things a bit less confusing
Reworked the terrain data load functionality and started working on heightAt
Still trying to get raycasting working.