Find a nice user interface (UI) to set the sections for each part of a song.

[ewjoachim]

This is the only editable thing in Part. It's logical to edit all the sections for all the parts in a Song simultaneously. A little bit of logic could help providing a default section for a part from its name ("Bass" usually is linked to Bass ...). We could examine all other parts named identically and if they're always linked to the same section, this should be the default choice.