Copied tnl-benchmark-spmv files and spmv.h from BLAS to SpMV. Deleted min/max size and stepFactor. Not working yet, backup purposes.

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.

Fixes #46

Added triad benchmark (copy to device, compute, copy to host) using different memory management strategies

fixes #23

fixes #21

Calculation of bandwidth broke in commit fb97bcd0

Check of MpiCommunicator::IsInitialized is necessary because
non-distributed benchmarks like tnl-benchmark-blas do not initialize
the communicator.