Implemented CUDA SharedPointer with CUDA Unified Memory. Does not work with sm30 and it is very slow.

* cmake:
  Added --offline-build option to skip update of external Cmake projects
  Disabled linking to the VTK library and enabled all mesh tests for CUDA even for nvcc
  Removed check for HAVE_CUSPARSE
  Declared all custom build options in CMakeLists.txt

* common-data:
  Re-enabled Python build in CMakeLists.txt
  Refactoring done - MeshDependentData was removed.
  Removing mesh dependent data.

It is not needed, since CUSPARSE is included in all versions of CUDA
since at least 7.0.

Also note that CUSPARSE is needed only for some tests and legacy code
(tnl-benchmark-spmv and wrappers in Matrices::CSR) and experimental code
(Preconditioners::ILU0). Everything is still guarded by the
HAVE_CUSPARSE macro, so the user can pass -DHAVE_CUSPARSE -lcusparse to
the compiler to enable the features.

This way they can use either yes/no, on/off, or true/false.

Implemented Array:containsOnlyValue.
Restored implementation of ArrayOperations::memoryCompare on host.

Implemented a method Array::checkValue which returns true only if there is an element with given value in the array.

I don't understand how it could work on the small grids...

Refactoring

See merge request mmg/tnl-dev!3

Content moved to src/Python/__init__.py.in

RAII is a thing :-P

New tests are in src/UnitTests/Containers/

New tests are in src/UnitTests/Containers/Multimaps/