change color of note velocity text (and don't set it or justification repeatedly...

change color of note velocity text (and don't set it or justification repeatedly); make pianoroll button2 clicks select correctly rather than always being additive; hide note velocity text as soon as the mouse moves. the color change will require remvoing ~/.config/ardour2/ardour3_ui.conf to become effective

git-svn-id: svn://localhost/ardour2/branches/3.0@7187 d708f5d6-7413-0410-9779-e7cbd77b26cf