This adds code to skip the rendering of bad points in vtkPlotLine
and vtkPlotPoints. Also allows adding additional bad points with
a mask array.

This is used by the plot-over-line filter in ParaView to skip
rendering of points which are not a part of the data set.

Change-Id: I70b5caadeb21a8080b34b6ca9b24dfcd4b0f19f6