Add a guitar edit mode that allows you to edit notes using a guitar controller

```
The plan is to use the strum bar to seek forward/backward by the grid snap 
amount and press the note buttons to toggle notes. Holding a note while seeking 
would create sustains.
```

Original issue reported on code.google.com by `xander4j...@yahoo.com` on 5 Nov 2010 at 8:42
