GW metainfo and parsing for exciting and FHIaims

@lucamghi @mscheidg @ladinesa I was working on GW for exciting and FHIaims:

• New GW metainfo with less but more meaningful quantities; exciting-specific quantities moved to the corresponding code metainfo.
• GW FHIaims correctly parsers GW for molecules, clusters, and solids.

TODO list:

• Include GW starting point and basis set as sections through the normalizer.
• Fix Fermi level in FHIaims #939 (closed)
• Include GW workflow in FHIaims.
• Re-organize GW metainfo and go through the exciting and FHIaims parsers.
• Update FilterRegistry.js and GUI tabs