Fix staff model IDs

First staff ID is now the parent container element (section), since a
<sb> shouldn't kick off the musical content.
Staffless Neume SVG

created drawings for the following neumes: gravis, oriscus, stropha,
punctum liq aug, porrectus liq dim, scandicus liq aug/dim, climacus liq
aug, torculus resupinus, torculus resupinus liq aug/dim, torculus
resupinus flexus, porrectus flexus, porrectus flexus liq aug, scandicus
flexus, scandicus flexus liq aug, pes subbipunctis, pes subbipunctis
aug