show both, velocity and gid, in note; when deleting note, move it out of the way so that the numbers are not visible

supported are now the following methods:
note create <step> <pitch> <velocity> <duration> <gid>
note delete <step> <pitch>
note change duration <step> <pitch> <duration>
note change velocity <step> <pitch> <velocity>

now we need to figure out how re-use ids of deleted (hidden) scalars

this reduces the number of scalars in the canvas and might improve performance