[media] Add cadencii.media.helper project
Add music-xml classes generated by xsd.exe

Command options are:
  "C:\Program Files (x86)\Microsoft SDKs\Windows\v7.0A\Bin\NETFX 4.0 Tools\xsd.exe" musicxml.xsd xlink.xsd xml.xsd /c /o:"directory_name"
.xsd files are downloaded from http://www.musicxml.org/dtds/
[vsq] Add MusicXmlWriter
Remove VsqFile::printAsMusicXml, use MusicXmlWriter instead
[vsq] Export tempo change
[vsq] Write correct xml header
[vsq] Fix bug: <alter> elements in <pitch> are not exported
[vsq] Add ISequenceWriter
Rename VsqxReader/VsqxWriter
Merge branch 'feature/export_music_xml' into develop
Update source header comments
[Cadencii] Add lock operation for AppManager.mDrawObject while drawing

Also change type of AppManager.mDrawObjects from Vector to array for safety
[Cadencii] Use AppManager.MAX_NUM_TRACK constant instead of integer literals
[Cadencii] Fix bug: crash when no UTAU singer is configured
[cadencii.helper] Update VisualStudio config: change output directory