feat(plugins/languages): improved `indepth` analysis and custom repo/sha

[lowlighter]

Relates #531 and #603

• [ ] Add new option plugin_languages_indepth_custom to manually specify:
  • [ ] Repositories
  • [ ] Commits sha
• [x] Instead of skipping unknown languages, group them together and display the number of "unanalyzed bytes"
• [ ] Find a way to check commits_authoring option inside commits body
  • git log --grep
• [ ] Create a new category to display "ownership accuracy", e.g:
  • 
  • • email in commit header/body
    • username in commit header/body
    • manually specified commits that could not be automatically attributed
• [x] Check commit signature with gpg key