bring back support for IServerPluginCallbacks v3 and v4

[markus-wa]

Hi I saw we had to revert 4e5ddf8 in 0e35864 due to #101

Are there any plans to bring it back?
This is a critical feature for us and we'd be happy to invest some time from our side to find a solution to avoid a fork, but would need some guidance on how to make this work (personally I don't have access to a Windows machine)

Could we conditionally enable them only for Linux or certain games?

[asherkin]

I'm unclear what this nets you, can't you hook the functions (at the dispatch point) regardless of if MM:S is opting in to the newer interface?

The path forward to un-reverting the change is primarily figuring out why it broke with the SDK2013 base engine, I don't know if that's been looked at yet.