Enhance bag plot API to allow specify line and points properties.

A new vtkPen is added to draw bag boundary lines, while the
default plot Pen is used to draw bag plot points.

This also patch the forced color values for Box plot pen.
Box plot pen is used to draw the box plot lines.

Change-Id: I566779743da52226916649879973699052366f28
Merge topic 'EnhanceBagPlot' into master

39efc956 Enhance bag plot API to allow specify line and points properties.