Update to add support for Layout Management

[n0toose]

This application does not use the Layout API. This results in weird behavior with cut-off text, as well as a lot of other visible quirks.

Certain important labels are also cut off, and the margins between objects are not sufficient:

The Control windows should be reimplemented, and the windows should be resizable.

[pulkomandy]

The "part" widget in the main view is sized not according to its contents, but according to the part length in the song. Otherwise things would be misaligned.

The volume sliders are intentionally stuck closely to the vumeters because they are grouped by channel.

The main window has only 3 views: the menu, the main view with all the parts, and the scrollbar. I think layout isn't really needed there. A better minimal size so that the menu is always fully visible would be enough.