Add table with ClinGen/ GenCC entity scores

[berntpopp]

For manual curation add a table with detailed ClinGen/ GenCC entity scores and curations.

TODO:

• find a source for this data
• compute a summary table
• consider adding this to the per gene subpages (e.g. issue Docs: Render bookdown pages with information for all genes #18)

[berntpopp]

Use this URL for ClinGen:
https://search.clinicalgenome.org/kb/gene-validity/download

Then perhaps parse the curation URLs in that file.
However, there are various SOPs that may be difficult to unify.