[Denemo-devel] Mouse use

[Richard Shann]

I've put in some code to make the mouse more useful in the dead areas of
the display. You can now navigate earlier in the score by clicking
before the first visible note, and you can access initial
clef/keysig/timesig editing by clicking on the relevant thing, and
staff/voice edit by clicking in the margin before the staff. Finally you
can get the score directives at the top left of the area. None of these
places were any use before.
I've started to develop some highlighting of these areas, too.
Also checked-in using Tab (or press-right mouse) to get edit object as a
standard binding (Default.cmdset and NumericKeypad.cmdset).

Richard