text.Shaper is not thread safe, which caused crash when adding
multiple VSTI plugins to a DAW project. This change fixes that
crash. Further refactorings need to consider where that text.Shaper
should actually reside.
send targets are now by ID and Song has "Score" part, which is the notes for it. also, moved the model part separate of the actual gioui dependend stuff.
sorry to my future self about the code bomb; ended up too far and did not find an easy way to rewrite the history to make the steps smaller, so in the end, just squashed everything.
