Add Basic support for ISteamGameServer_UserHasLicenseForApp

[hZeper]

Some games host server in the background when playing in solo/private games and use the ISteamGameServer_UserHasLicenseForApp instead of the ISteamUser_UserHasLicenseForApp to check if the user owns a specific piece of DLC.

This very basic implementation need some clean up/change at steam_api_flat.cpp#L265 before mergin.

Tested working on appID 1604030 in proxy mode.