Automatic adjustment of staff heights in display

[Richard Shann]

I've overhauled the code controlling how much space is allowed for
staffs in the display. Except for the space above the top staff (which
can be controlled as before with the mouse wheel or by setting it in
the staff properties) the space allowed is now computed while the
staffs are drawn.
This is quite a radical overhaul of very ancient code - please check
that nothing you use is broken by it.

Richard