The benchmarks, examples, tools or Python bindings are not run by the CI, so
we just check that they can be compiled. But we don't have to do it twice...

- There is an RAII wrapper called ScopedInitializer to handle
  finalization due to C++ exceptions and to avoid calls to Finalize in
  all exit branches.
- Fixed signature of MpiCommunicator::Init to match that of MPI_Init.

Even the methods for specializations without storage have to return
something, which was not the case...

The original was simpler/more readable and we require GCC 5.0 now.

This reverts commit d920a278.

The std::isnan method can be safely used in host code (if the compiler
is not moron). There is no device code which uses isnan so the
TNL::isNan function is useless.

This reverts commit 0eff2f63.

This shuts up a lot of GCC warnings...

* cineca/refactoring:
  Moved simple examples from tests to examples
  Removed explicit template instantiation of vector operations
  Removed explicit template instantiation of small templates
  Reordered methods of Array to group similar methods together
  Renamed ElementType to ValueType and Element to Value
  Removed Array::touch method

This is closer to value_type which is used in STL containers.

It has not been implemented in the past decade so it can be safely
assumed that it is useless.