New mesh readers/writers, Grid and DistributedGrid refactoring

See merge request !97

It was replaced with PVTIWriter and PVTIReader.

- pointer from Grid to DistributedGrid is gone, instead the
  DistributedGrid has a localGrid attribute
- Grid has new attributes: localBegin, localEnd, interiorBegin,
  interiorEnd (useful for traversers)
- all tests work except for CutMeshFunction

DistributedGrid: added methods setGhostLevels and getGhostLevels for compatibility with DistributedMesh

Setting up a distributed grid will be solved with a mesh reader via the
function loadDistributedMesh.

Notes:

- saving and loading distributed mesh functions is commented out in
  various problems - PVTI reader/writer is needed
- disabled compilation of DistributedVectorField and DistributedGridIO
  (the tests were already broken and not executed anyway)

Notes:

- saving the distributed grid in DistributedGridIO_MeshFunction.h was
  commented out - it was probably just for debugging anyway...
- MPI stuff in tnl-init is commented out - PVTI reader/writer is needed
- loading of a distributed grid is commented out in the specialization
  of loadDistributedMesh - PVTI reader is needed

- tnl-lattice-init was intended only for the tnl-lbm project which is
  deprecated (did not lead anywhere)
- tnl-view has become obsolete, since all mesh functions are going to be
  saved directly in the VTK/VTU/VTI format and thus the conversion from
  .tnl files is not necessary

Both tools were moved to the tnl-legacy repository:
https://mmg-gitlab.fjfi.cvut.cz/gitlab/tnl/tnl-legacy

The exception is raised from Config::ParameterContainer::getParameter