Feature: Simplification of charts

I'd like the ability to simplify charts by reducing or eliminating substitutions and passing chords -- essentially to bring out the "vanilla book" changes. This would require some form of annotation. (The goal would be detail hiding, analogous to how Google Maps makes small roads disappear until you zoom in.) It could be done by:

* Letting me flag the important chords, and displaying them in a different color, or optionally hide the 'less important' ones
* Letting me rename chords
* Automatically identifying chords that are likely to be 'less important' (e.g. because they last for a short time) and letting me decide whether to hide them
* Automatically renaming chords by family (major, minor, dominant, etc.) and hiding the details (again letting me decide what to keep)

This would all be simpler if an "arranger's workbench" mode could be provided, in which we can manipulate a chart with various interactive and automatic tools.

Not a trivial feature extension, but this is more or less what we all do when we start with somebody's chart and work it up for the band, simplifying/correcting here and adding/substituting there.