GUI layout: subwidget sizes

Revise the entire mechanism for setting subwidget sizes.

• Script window should have fixed width so that 100 or 120 chars can be shown without horizontal scrolling.
• Sample and instrument editors currently have fixed maximum width; should they use the entire window? (#994 (closed))

changed milestone to %post-22-cleanup

added GUI inconvenient UI labels

mentioned in issue #994 (closed)