Fix alignment of unstyled text.

Separate out the offset from the text alignment, and use the
text alignment to set the bounding box.
Fix shape and initial position.
Merge pull request #312 from softins/unstyled-text

Fix alignment of unstyled text.
minor/typo fixes
update MusicXML website in about box
fix #20997 fix #19149
fix #15943: Tuplet creation from empty measures (whole rests)