Add Teamspens HammerAddons

[sheepy676]

I am currently working on a campaign for ReactiveDrop and find it a little annoying when the game updates to find that I have to replace the fgd with a improved one from Hammer Addons, there currently isn't an improved fgd for ReactiveDrop specifically but there is one for Alien-Swarm. What I did to get this improved fgd is take the Alien-Swarm version and add all the ReactiveDrop entities to it and improving where I could by editing the fgd since I don't know python.

I suggest that ReactiveDrop adds Hammer Addons and moves over to using that system for the fgd; this would greatly improve the mapping experience and make making maps easier. I for one find it hard to map without it since it makes all the entities be consistent in their keyvalues.