Replaced reativecocoa submodule w/ ReactiveCocoa pod

Rationale: The existing reativecocoa was way out-of-date, using Cocoa GC instead of ARC.

• Deleted `.gitmodules` file and `lib/reativecocoa` Subproject-file-thing.
	» You may still need to do a `rm -rf .git/modules/lib/reactivecocoa` in your local repo (see: http://stackoverflow.com/questions/1260748/how-do-i-remove-a-git-submodule).
	• Removed `ReactiveCocoa.framework` references and `lib/reactivecocoa/…` Framework Search Path
• Set up the project for CocoaPods, adding `$(inherited)` where CocoaPods said we should.
• Added the `ReactiveCocoa` pod.
Updated to use more-modern ReactiveCocoa

• Updated `rac_signalForKeyPath:onObject:` calls to `rac_signalForKeyPath:observer:`, which happened in ReactiveCocoa 0.16.2.
	» See https://github.com/ReactiveCocoa/ReactiveCocoa/compare/v0.16.1...v0.16.2 , especially NSObject+RACPropertySubscribing.m
	» Seems to have been originally written for ReactiveCocoa 0.14.0 or some version around there.
Switched to ReactiveCocoa 1.x

• Switched to the last/latest in ReactiveCocoa's 1.x series, 1.9.7, in order to avoid the API changes (and deprecation warnings) that look like:
	◦ `'rac_signalForKeyPath:observer:' is deprecated: Use -rac_valuesForKeyPath:observer: or RACObserve() instead.`
	» I personally don't really know anything about ReactiveCocoa, so I'd rather just keep it working as it was than try to update it.