Add stämsång

Add a tab under Sånger which allows users to add harmonic notes to song texts.

- Should be able to choose Bas, Tenor, Alt, or Sop
- Should be able to play first note or the whole melody

Start by locating the Sånger tab and the code that displays song texts. Trace how a song's notes are represented and how playback currently works, if supported. Done means users can choose Bas, Tenor, Alt, or Sop, add harmonic notes to song texts, and play either the first note or the whole melody.

Vom Indexierungsmodell aus dem Issue-Text verfasst.