Improve defaults for InstrumentSwitch

Improve defaults for InstrumentSwitch

-) Don't use a staff-padding of 2 (too far from the staff!), but rather 0.5
-) Left-align cue instrument names on the note they apply to (common practice
   is to left-align at the beginning of the measure, or sometimes even further
   to the left depending on the vertical extents of the cue voice).
   Center-aligned instrument names lead to all kinds of broken spacing, i.e.
   the first note will only start at half the width of the cue instrument
   name, even if that means a huge horizontal empty space!.
-) Add outside-staff-priority, so that collisions are automatically handled
-) Adjust extra-spacing-width to prevent ugly stretching of notes when
   beams got far above the staff

Okay'd by Joe Neeman on lilypond-devel

Signed-off-by: Reinhold Kainhofer <reinhold@kainhofer.com>