Dedicated server with Steam is a joke

I’ll do a pull request on the Unreal Engine repository, and then a wiki post. Basically I added a variable on the GameMode (bUseAuthentication) that if is set to true, enables the Steam authentication code.
I didn’t it because I wanted to do a complete system well coded, but now I’ll do this pull request, so anyone that wants to have a workaround to the Steam authentication, can have it.