reformatting, removing some comments that are irrelevant to plugin
framework in a way that DoxyGen should still find them, documenting the
enums and fully qualify all types that are specific to MuseScore,
adding semicolons for Q_DECLARE_METATYPE() and
Q_DECLARE_OPERATORS_FOR_FLAGS(), removing semicolons from Q_PROPERTY()
(QtCreator complains about them) and fixing a comment, reformatting for
alignment