Split up structure
Fix typo
Get rid of jsjs and replace it with iframe eval
Define a couple of basic math utilities
Move sandbox to a module of its own
Load math module to sandbox
Wrap math module in define
Remove extra boilerplate from examples

We don't need that since we control the boilerplate. It is better to keep it
simple.
Change editor to use a realistic code example
Add initial stubs for cube API

The idea is that the sandbox executes the script and tracks operations
executed. After that they will be converted into WebGL commands and displayed
in the preview.
Make cube().off() work