Adding client libraries for MonoTouch, Mono for Android

This adds client libraries for MonoTouch and Mono for Android. The changes here are pretty minimal, and mostly just consist of some `#ifs` in a few of the same places Windows Phone needed them. The other modifications were to work around cases where JSON.NET's `JToken.Value<T>()` call would cause the MonoTouch client to crash due to JIT.

For now I'm only including the libraries themselves, and leaving them out of the main solution files to limit the disruption.