[UX issue] multiple GFF

[DrYak]

There are multiple places to specify GFFs in V-pipe and this is confusing to users.

• section input, property gff_directory : a directory with multiple GFFs used for the visualisation
  • visualisation supports using multiple GFF, e.g.: for genes/open reading frames, for mature product/proteases-clived, for domains on the proteins.
• section input, property metainfo_file : a YAML file giving extra information about the GFF inside the directory above
  • as it is used only for visualisation, the metainfo is free-form.
• section frameshit_deletions_checks, property genes_gff : a single GFF, specifically gens, used only by QA.
  • this one is currently completely different from the visualisation's ones.

All this leads to confusions for users, see here

[DrYak]

Fixed in #58a9cccca3bf25021a016031f19f0816db748f44

• GFFs are now all centralised in the same section: [general]
• If a Genes-specific GFF isn't explicitely provided, V-pipe will try to autoselect one among all the visualisations GFFs (based on names)