More SI on L4D

I have adjusted the SI plugin from L4D2 so that it works in L4D now too.
There were far to less SI on the map before.
One player alone could easily walk through the map and reach the safe house alone.
Now you should stick together and help each other against the SI.

One drawback is, that L4D does not have enough different SI.
So the same kind will spawn often twice (because the random logic can only choose from 3 different types: boomer, hunter, smoker)