Game meta key

[nikuda]

To be able to support 'genre' and similar meta information schema needs to change to hold genres at the name level, as you don't want to re-tag every clone/reimplementation.

# Before
- name: Dune
  clones:
    - name: OpenDune
      genre: Real-Time Strategy
    - name: Dune Legacy
      genre: Real-Time Strategy
  reimplementations: ...

# After
- game:
    name: Dune
    genre: Real-Time Strategy
    theme: Sci-Fi
  clones: ...
  reimplementations: ...

[nikuda]

Simpler solution implemented in #358 (comment)

- name: Cataclysm
  meta:
    genre: [Role-playing]
    subgenre: [Roguelike]
    theme: [Horror, Survival]
  clones: ...
  reimplementations: ...