Refactored next element command.
	modified:   libmscore/chord.cpp
	modified:   libmscore/element.cpp
	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:   libmscore/segment.cpp
	modified:   libmscore/system.cpp
	modified:   libmscore/system.h
	modified:   mscore/scoreview.cpp