Handle cases where Steam game could have multiple appid possibilities.

[Jozen Blue Martinez]

Some games can have multiple Steam appids, can probably just assign (symlink?) to every appid reported by the API.
People who bought games before an appid is retired can still have the older app in their library instead of the new one, assets are usually blank too.

Some examples:

• Arma II [33900, 33910]
• Battlefleet Gothic: Armada [317000, 363680, 450770]
• Dragon Age II [47900, 99809, 1238040]
• Aion [29640, 29660, 373680]

[Manos Paterakis]

This can now be done via 30d634a.