treer/plot: accept extra parameters
treer/plot: accept extra parameters

They allow to place new tree plots anywhere on the X axis.
Signed-off-by: Jean-Yves Tinevez <17c1793fcc6179ec3ae6319887e209161427f317@gmail.com>

tinevez/jyt-matlab,tinevez/jyt-matlab,tinevez/jyt-matlab,tinevez/jyt-matlab,tinevez/jyt-matlab