Add GameModeModel to add/control GameModes more easily

Essentially a list of decks for a game to use. I envision just picking from a list of Game Modes, which sets all decks, swaps all cards as necessary, adds icon to map, etc.

Meant to replace the convoluted methods of GameSetup.setGameMode

Example GameModeModel entry:
```
{
"id":"absol",
"tech_deck": "absol_tech_deck",
[other_decks],
"iconFile": "absol.png",
"description": "Absol's Overhaul Mod - Agendas/Relics/Techs/Mechs",
"homebrewHubLink": "https://discord.com/channels/743629929484386395/1215827226302349393",
"headerImage": "https://media.discordapp.net/attachments/1215827226302349393/1215875850025701457/modcover.jpg?ex=66079220&is=65f51d20&hm=ea254389be77dad07d7d3a496bb5c3f41fd8dfc0c045f03a0c41ce029acf7a1a&format=webp&width=346&height=554&"
}
```