Optimizations, UI tweaks

# Reorganization
- Moved SubD code out to a new file subd.js.
- Moved TODO list and notes out to a new file notes.md.

# Performance
- Updated to three.js 67dev
- Switched from three.js Geometry to Geometry2.
- Optimized three.js WebGL sprite submission
- Micro optimized the QuadEdgeMesh.
- Only rebuild geometry when changing smoothing level, not when toggling wireframe.

# UI
- Added model toolbar.
- Tweaked camera movement.
- Pulled sprites towards camera