Fix alignment of unstyled text.

Separate out the offset from the text alignment, and use the
text alignment to set the bounding box.
Small fixes
GUI panel for MIDI import
Automatically show MIDI panel on drop midi file
Fix tests build error
Merge pull request #325 from trig-ger/midi_gui

MIDI Import Panel
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