Merge pull request #168 from janek-warchol/display-path

display path to lilypond command in "engrave custom" dialog
add a name attribute to LilyPondInfo, defaulting to "LilyPond"
add prettyName() method to LilyPondInfo
use average clicking speed in Tap Tempo button in score wizard, auto-resetting after 3 secs; resolves #196
hopefully fix some error messages in the MIDI stuff on Mac OS X
crop 'out/bin/lilypond' from path displayed in "engrave custom"

this is a follow-up to 59f54df181d3d24be79387eaedec3c89faaa4e31.
Since out/bin/lilypond is in 99.9% cases redundant, lets not
allow it to clutterr the view.