Add support for Github multi game collections

[cahudson94]

Adds definitions to the mod.yml file for the following fields:

• isCollection: boolean for if the specific mod install is actually a collection (ie contains multiple games worth of info)
• collectionGames: string list of the games that have mods included
• asset.game: string to specify which game the script belongs with

This allows for the install and update of collection based mods from Github using the above tags in the mod.yml as well as the update and auto update of said installed mods. Creates a parent folder called collections on the same level as the game specific folders. And cleans up any installation of the mod that happened before it became a collection.

[TopazTK]

Good shit.

[Delta-473]

Can you maybe add some info to the documentation on how to make collections? And an unit test or 2 are always nice, you can add it in the follow up pr #1176 if you want.

[cahudson94]

Yeah, I was looking at the docs a bit. I will go ahead and do it on that branch.