Vcs dv3d separate plot constituents updated

Adds dual input scalar plots and enables separate configuration of plot constituents (e.g. surface, volume, slice).

Must also merge Vistrails branch:     uvcdat-dv3d-Fix_parameter_issues
@ThomasMaxwell it would probably be worth at some point to use 
VCS_validation_functions.isNumber instead. No need to duplicate these sort of things. No big deal.