Add models (Overlay, OverlayChannel)

[alma3lol]

This should add these models:

• Overlay that has the following properties:
  • name (string)
  • type (enum) [GAME, NEW_SUB, LATEST_SUBS, NEW_FOLLOW, LATEST_FOLLOWS, NEW_GIFTED_SUB, LATEST_GIFTED_SUBS, NEW_CHEER, LATEST_CHEERS, NEW_REDEEM, LATEST_REDEEMS]
• OverlayGame that has the following properties:
  • overlay_id (int) (Overlay ID).
  • channel_id (int) (Channel ID).
  • game_id (int) (Game ID).