Fixing iOS build after reorganization

Some sources in moai-iphone looked like they should be in separate build targets, such as MOAIFacebookIOS => libmoai-ios-facebook, but some seem like iOS-specific additions to targets; like MOAIGameCenterIOS => libmoai-ios, or MOAIHttpTaskNSURL => libmoai-ios-http-client.

I split those sources into separate targets where it made sense, and ended up with a set of targets like this:

![Xcode targets](https://www.evernote.com/shard/s59/sh/655b0232-ae2d-4089-b6a7-4db90510241c/ec234f6861ed981662f9dc56bf567f88/res/fbc1c80b-7439-41b9-8162-5c2ae46088b1/skitch.png)

What is the role of libmoai-ios-3rdparty supposed to be? Is it supposed to be a "give me all of the 3rd-party stuff I might want" target, or just the basics that are necessary for using Moai?

Also, I'd like to generate as much of this as possible through CMake, but I have limited experience writing CMake stuff, so maybe @franciscotufro could help with that.

@patrickmeehan