LWAVE: selfconsistent GW

If LWAVE=.TRUE. is set explicitly in the INCAR file, the WAVECAR file is updated after the GW calculations, and the updated QP-energies are written to the file. This allows to perform selfconsistent GW instead of G$_0$W$_0$ calculations. Note that only the energies are updated, whereas wavefunctions are kept constant on the DFT level.