Switched to ReactiveCocoa 1.x pod

* Switched from using a submodule to the ReactiveCocoa 1.x (currently 1.9.7) CocoaPod.
    * In the process, updated the project for CocoaPods.
* Updated ReactiveCocoa syntax a touch for great better compilation (`rac_signalForKeyPath:onObject:` calls to `rac_signalForKeyPath:observer:`).