remove indices in C++
Change python gf after removal of c++ indices

I also did some cleaning. I removed the gf_generic.pyx which is not
necessary at this stage.

  deleted:    pytriqs/gf/local/gf_generic.pyx
  modified:   pytriqs/gf/local/__init__.py
  modified:   pytriqs/gf/local/gf.pyx
  modified:   pytriqs/gf/local/gf_generic.py
  modified:   pytriqs/gf/local/gf_imfreq.py
  modified:   pytriqs/gf/local/gf_imtime.py
  modified:   pytriqs/gf/local/gf_legendre.py
  modified:   pytriqs/gf/local/gf_refreq.py
  modified:   pytriqs/gf/local/gf_retime.py
  modified:   pytriqs/gf/local/imfreq.pxd
  modified:   pytriqs/gf/local/imfreq.pyx
  modified:   pytriqs/gf/local/imtime.pxd
  modified:   pytriqs/gf/local/imtime.pyx
  modified:   pytriqs/gf/local/legendre.pxd
  modified:   pytriqs/gf/local/legendre.pyx
  modified:   pytriqs/gf/local/refreq.pxd
  modified:   pytriqs/gf/local/refreq.pyx
  modified:   pytriqs/gf/local/retime.pxd
  modified:   pytriqs/gf/local/retime.pyx