Add capabilities for SMTK inside ParaView.

+ Create a new VTK source that reads SMTK model files.
+ Add a selection manager to smtk::resource that, unlike the
  smtk::extension::qt::qtSelectionManager, tracks ResourceComponents
  instead of EntityRefs, MeshSets, and DescriptivePhrases.
+ Add the husk of a ParaView stand-in for the resource manager,
  which does not yet exist, to act as a client-server glue layer
  for selection management.
+ Add a ParaView behavior to synchronize the selection
  (a) between ParaView's server-side per-block selections on SMTK
      representations; and
  (b) across the client-server connection using ParaView's pqSelectionManager.
+ Add a ParaView tool bar exposing buttons to filter the SMTK selection.
+ Rename the smtk::extension::SelectionModifier enum to smtk::resource::SelectionAction.
+ Change _all_ the `vtkModelMultiBlockSource` outputs to be multiblocks;
  The glyph mapper accepts multiblocks of vtkPolyData instances
  for the glyph points, so we should keep each instance's placements
  as a separate block. This makes it possible to use the new mapper
  pickability features with instance placements, too.