Provide information on plot input data range.

This commit provides an interface for querying the
range of values taken on by a vtkPlot's X- and Y-axis
inputs.

This can be used to determine whether log-scaling
is appropriate for each axis of the plot. It is part
of a fix to ParaView bug 13899.

Change-Id: Ia0449ca496dd935fb4ca25dc5dd2b691d2f89d93
Merge topic '13899_log_axis_warning' into master

6f8f8037 Provide information on plot input data range.