Add way to control vibrato timing

[jonikorpi]

Vibrato is sometimes delayed, instead of starting right off the bat.

This is a bit tricky to pull off. Simply increasing its attack doesn’t work: there needs to be a hold time preceding it. Its attack also needs to be increased though, since an instantly starting vibrato at after a hold time sounds off, unlike when it’s at the start of the note.

Does it also need controls for its decay (doesn’t exist right now) and a release?