BSE and XANES metainfo

@ladinesa let's work on the parsers, metainfo and GUI directly on this super-issue. @lucamghi this is useful for you too, please keep an eye of this.

I'll divide a bit the workflow so we can use it to keep track of the smaller features:

• Parsing and metainfo:
  • Create method.bse and method.core_hole metainfo.
  • Refactor calculation.excited_states to calculation.spectra. Create type quantity to differentiate the type of spectra (EELS, XANES, ARPES, EDC...).
  • Parse BSE in exciting.
  • Parse BSE in OCEAN in electronic-parsers.
  • Create parse for XSPECTRA in workflow-parsers.
  • Parse electronic spectra for all the afore-mentioned parsers.
• Fix #1411 (closed) -> using try/except for automatic workflow recognition.
• Re-visit method.bse and coordinate with Nathan for method.core_hole #1371 (closed) .
  • Define a base class ExcitedStateMethodology which contains metainfo common to Screening, GW, BSE, TDDFT calculations: this will contain mesh subsections (K, Q, Frequency), broadening, n_states and n_empty_states quantities.
  • Inherit this in Screening, GW and BSE.
  • Use Screening as subsection of GW and BSE.
  • Use CoreHole as subsection of BSE.
• Method normalizer.
  • Add BSE and DFT+BSE normalizer.
  • Generalize GW, DFT+GW.
  • Add tests for BSE.
• Adapt CoreHole metainfo from #1371 (closed).
  • Add tests for CoreHole.
  • Add CoreHole normalizer.
• Spectra normalizer (#1506 (closed)).