Moved (most of) static methods from TNL::Devices::Cuda as free functions into separate namespace TNL::Cuda

The class TNL::Devices::Cuda was too bloated, breaking the Single
Responsibility Principle. It should be used only for template
specializations and other things common to all devices.

The functions in MemoryHelpers.h are deprecated, smart pointers should
be used instead.

The functions in LaunchHelpers.h are temporary, more refactoring is
needed with respect to execution policies and custom launch parameters.

Reference: https://stackoverflow.com/a/23766303
Documentation: https://cmake.org/cmake/help/latest/command/install.html#installing-directories

Added macro TNL_MPI_PRINT_COND for conditional print outs.

Reimplemented Config::ConfigDescription and Config::ParameterContainer using std::vector instead of TNL::List

This is much safer and simpler because it solves many problems due to
cyclic inclusion of TNL headers.

- 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.

Added assertions to MpiCommunicator.h checking that MPI functions are not called with the null group