Autodetect number of players supported

[eniklas]

See if you can query something like IGDB or Mobygames to get this info.

[eniklas]

https://api-docs.igdb.com/#multiplayer-mode looks promising.

[eniklas]

This is done as of 8cec957, still need to test.

[eniklas]

This is working for Steam games with IGDB. Max players for a title is determined in this order of precedence:

• max_players in the config yaml
• max players from IGDB (the highest value found for any multiplayer game mode)
• 1 if the above aren't available and the only game mode from IGDB is single player
• 0 (unknown) otherwise

Options have been added to the web UI and CLI to include or exclude 0-player games.

I'll go through the multiplayer games that don't have max players in IGDB and contribute those numbers to IGDB where possible, and add them to the config file otherwise.

I'll open a separate issue to look into getting data for other platforms.