Move lattice C++ code to triqs directory

Moved the C++ code for the lattice in the triqs subdirectory
where it should be. Also deleted an obsolete k_omega.hpp
file. Fixed CMakeLists accordingly

  modified:   pytriqs/base/lattice/CMakeLists.txt
  renamed:    pytriqs/base/lattice/C++/wrap.cpp -> pytriqs/base/lattice/lattice_wrap.cpp
  renamed:    pytriqs/base/lattice/C++/bravais_lattice_and_brillouin_zone.cpp -> triqs/lattice/bravais_lattice_and_brillouin_zone.cpp
  renamed:    pytriqs/base/lattice/C++/bravais_lattice_and_brillouin_zone.hpp -> triqs/lattice/bravais_lattice_and_brillouin_zone.hpp
  renamed:    pytriqs/base/lattice/C++/concepts.rst -> triqs/lattice/concepts.rst
  renamed:    pytriqs/base/lattice/C++/functors.hpp -> triqs/lattice/functors.hpp
  renamed:    pytriqs/base/lattice/C++/grid_generator.hpp -> triqs/lattice/grid_generator.hpp
  renamed:    pytriqs/base/lattice/C++/tight_binding.cpp -> triqs/lattice/tight_binding.cpp
  renamed:    pytriqs/base/lattice/C++/tight_binding.cpp.new -> triqs/lattice/tight_binding.cpp.new
  renamed:    pytriqs/base/lattice/C++/tight_binding.hpp -> triqs/lattice/tight_binding.hpp
  deleted:    triqs/gf/k_omega.hpp