Add a parameter set node and rework the output plot chart and series …

…nodes.

Use multiple parameter nodes:
 - generated in a combobox handling vtkMRMLScriptedModuleNode nodes
 - intended to group a centerline/surface input pair: one pair, one parameter
 node
 - group outputs: one table and one chart for one parameter node
 - restore pre-computed results when a parameter node is selected

Improve handling of the plot series:
 - do not enforce the name of a plot series node
 - synchronize the plot chart with the parameter node
 - keep the display of a single series in a chart

Remove unused variables, functions and comments.