Making RACEventTrampoline and RACDelegateProxy available in the iOS library

I started using RAC only recently, so I might be missing something really basic, but there was no way for me to access and use RACEventTrampoline and RACDelegateProxy. I'm pretty sure I got the whole project (build phases, dependencies, etc.) configured properly. 

This what's in the pull request, is the only way I could get it to work. The aforementioned two classes were available after making these changes.