Add DataModel to StandAlone group.
Add DataModel to StandAlone group.

This make it easier to build editions which just include DataModel and
dependencies. DataModel module gets included in a "StandAlone" build of
VTK since several other modules in the StandAlone group depend on
DataModel. However, if the edition only has DataModel (and none of the
other modules that depend on it), it doesn't get enabled by default.
Given our definition of "StandAlone" module, DataModule should indeed be
a part of it. Hence, adding it to that group.

keithroe/vtkoptix,keithroe/vtkoptix,sumedhasingla/VTK,sumedhasingla/VTK,SimVascular/VTK,keithroe/vtkoptix,sumedhasingla/VTK,sumedhasingla/VTK,SimVascular/VTK,sumedhasingla/VTK,keithroe/vtkoptix,SimVascular/VTK,SimVascular/VTK,sumedhasingla/VTK,SimVascular/VTK,keithroe/vtkoptix,keithroe/vtkoptix,sumedhasingla/VTK,SimVascular/VTK,SimVascular/VTK,keithroe/vtkoptix,SimVascular/VTK,sumedhasingla/VTK,keithroe/vtkoptix