Fixed some GUI bugs. Arranger GUI temporarily fixed.

Fixed some GUI bugs. Arranger GUI temporarily fixed.

The scroll group widget is beyond repair. I tried
my best to make it do what it should be doing by
using kludges and an almost trivial subclass. The
bottom line is that the scroll group widget is broken.

Details: When the scroll group is manipulated, it does
not call its own callback. It does call relayout on
its children. However, when the window is maximized,
the scroll group itself does not fully relayout itselt
correctly. In corrects itself if it scrolls twice more.
In some circumstances the scroll group will get caught
in a strange loop if the children are at the very edge
of the scrolling region, and fooling with it enough
will fix it, but it is still broken. In this program,
maximize, scrollTo, and other factors lead to graphical
breakage.

The scroll group widget will be dumped in a new branch
soon. It will be replaced with two scroll bar widgets
that simply use the regular callback api, which the
scroll group should be doing, and control the main
canvases just like layout was controlling the timelines,
event editor, virtual keyboard, and track info.