Code cleanup
 Fix errors in plot examples
 Refactoring
 Preliminary version of GUI for the generation of the (energy dependent) GW scissor.
 Document new methods.
 First version of sigresviewer (WX Gui)
 Add new files.
 Adding support for wx.Grids (useful to show QP results)
 Add toolbar button for plotting KS energies with QP markers.
 Use more re-usable wx.frame for plotting band energies with markers.
 Add fatbands plot for electrons (python version, netcdf data is still missing)
 Move kpoints stuff to abipy.core
 Refactoring
 Automatic refactoring introduced changes unrelated modules (fixed in this revision)
 Cosmetic changes.
 Automatic recognition of special k-points in bands.plot (use pymatgen database)
 Fix several regressions due to the previous refactoring
 Automatic labels for q-points in phonon plots.
 Made PhononBands interface more similar to the one used for ElectronBands.