fix(exports): export Vexflow graphical classes (e.g. VexflowGraphicalNote)
fix(exports): export Vexflow graphical classes (e.g. VexflowGraphicalNote)

part of #549

opensheetmusicdisplay/opensheetmusicdisplay,opensheetmusicdisplay/opensheetmusicdisplay,opensheetmusicdisplay/opensheetmusicdisplay