Setting up files and directories for in-situ classes.

Started implementing mesh node coordinates wrapper.

Conflicts:
	CMakeLists.txt
Implementation of read only methods and a simple test.

There is lots of boilerplate code which is required, see also
https://github.com/Kitware/VTK/blob/master/IO/Exodus/vtkCPExodusIINodalCoordinatesTemplate.h
Renamed ti *-impl.h
Adding namespace InSituLib.
InSitu tests are always build now.
tmp.
VtkMappedMesh should be complete.

Conflicts:
	CMakeLists.txt
	Tests/CMakeLists.txt
Initial implementation of VtkMappedMeshSource.
VtkMappedMeshSource is working.

Remaining todo: point and cell data.
Some comments and cleanup.
Added a mesh conversion round trip test.

It takes an OGS mesh, converts it via VtkMappedMeshSource to VTK, then
the VTK mesh gets converted back to OGS mesh.