WebSocket polyfill

Summary:
- Added as a library in /Libraries/WebSocket
- Drag and drop to add to project (similar to adding Geolocation polyfill)
- Exposed as `window.WebSocket` which conforms with https://developer.mozilla.org/en-US/docs/Web/API/WebSocket specs
Closes https://github.com/facebook/react-native/pull/890
Github Author: Harrison Harnisch <hharnisc@gmail.com>

Test Plan: Imported from GitHub, without a `Test Plan:` line.

React.podspec

@@ -98,8 +98,9 @@ Pod::Spec.new do |s|
     ss.preserve_paths   = "Libraries/Vibration/*.js"
   end
 
-  s.subspec 'RCTWebSocketDebugger' do |ss|
+  s.subspec 'RCTWebSocket' do |ss|
     ss.dependency         'React/Core'
-    ss.source_files     = "Libraries/RCTWebSocketDebugger/*.{h,m}"
+    ss.source_files     = "Libraries/WebSocket/*.{h,m}"
+    ss.preserve_paths   = "Libraries/WebSocket/*.js"
   end
 end