Subclassed ElementAccessibilityInfo for Markers, Jumps and Measures.
	modified:   libmscore/jump.cpp
	modified:   libmscore/jump.h
	modified:   libmscore/marker.cpp
	modified:   libmscore/marker.h
	modified:   libmscore/measure.cpp
	modified:   libmscore/measure.h
	modified:   mscore/menus.cpp