The Model was getting unmaintanable mess. This is an attempt to refactor/rewrite the Model so that data of certain type is exposed in standardized way, offering certain standard manipulations for that data type, and on the GUI side, certain standard widgets to tied to that data.
This rewrite closes#72, #106 and #120.
The old "native" compiler bridged version is now started with cmd/sointu-nativetrack,
while the new pure-Go bytecode implemented bytecode interpreter is started with
cmd/sointu-track
Thus, you do not need any of the CMake / cgo stuff to run cmd/sointu-track
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.
