Include new BandGap in GW

Please, @himanel1 @ladinesa @ndaelman (@jrudz , you can also check this out). This is part of the new BandGap definition @ndaelman did, and fixing the issue with the GW workflow.

This is mainly a fix, but I also took the change to reorganize a bit the ResultsNormalizer into abstraction (similar to MethodNormalizer). Can you please check this (if possible to be merged before the reprocess, i.e., by the end of the week) and give feedback? We can later extend changes to other results.properties sections.

There is a related minor PR in github: https://github.com/nomad-coe/electronic-parsers/pull/93

Closes #1459 (closed)