Prune "legacy" code

[bobbicodes]

Because I started building this without really knowing what I was doing, and ended up trying out dozens of features before converging on an effective few, there remains much vestigial code (entire namespaces, even) that I feel would best be removed, saving it for future projects and refocusing this one on what it has become - a cute, multitimbral sample-based scrolling music editor.

This "legacy code" includes:

• Western music notation components (currently only using the staff)
• Numerous unused SVG components (characters, etc.)

Code related to features currently being worked on (MusicXML import, etc.) should be moved to separate feature branches.