"greg" version of firewalker shoe code

A few improvements to the firewalker code

- Adds DEBUG option to allow previewing without wearing.
- Changes how LED indices are mapped to allow for LED strip running other way around shoe. 
- Creates MODE_RAINBOW_FALLBACK to have a default mode for if sensors break.
- Adds MODE_GREEN because Greg's other glow stuff is always green.
- Some formatting changes because I don't like when logical chunks of stuff don't have linebreaks between them.