Expose AbstractMeshStruct from discretization interface.

This allows external access to the workset CellTopologyData instance.
Add VTK in-situ data objects for Catalyst CoProcessing.

Add a set of data containers that mapped the Albany/Trilinos data
containers into the vtkDataArray and vtkUnstructuredGridBase APIs.

* Albany::Catalyst::Decorator: AbstractDiscretization implementation that
  creates a (currently unused) vtk data structure from the mesh.
* Albany::Catalyst::Grid: vtkMappedUnstructuredGrid implementation using
  the AbstractDiscretization API.
* Albany::Catalyst::TeuchosArrayRCPDataArray: vtkMappedDataArray subclass
  using Teuchos::ArrayRCP for nodal coordinates.
* Albany::Catalyst::EpetraDataArray: vtkMappedDataArray subclass using
  Epetra_Vector for nodal scalar attributes.
* Albany::Catalyst::Adapter: Handles communication between Albany and
  the Catalyst library.
Merge branch 'catalyst'

Merge in AbstractDiscretization decorator developed by
Kitware to support Catalyst in-situ visualization.
Fix misc test issues.