Adding [super initialize] to correct misreporting by MDCD

Summary:
In working to remove dead code from the code base, we identified that a number of classes that subclassed `RCTEventEmitter` were being reported as unused when they are in active use.  That was due to a lack of a `[super initialize]`.  This diff adds the call to super.

Changelog:
[General] [Added] - Call to `super` in `+initialize` of `RCTEventEmitter`

Reviewed By: javache

Differential Revision: D19727783

fbshipit-source-id: 19c6c7f08e7a8b2f764988fdfcd70f92dbf1b74b

React/Modules/RCTEventEmitter.m

@@ -24,6 +24,7 @@ + (NSString *)moduleName
 
 + (void)initialize
 {
+  [super initialize];
   if (self != [RCTEventEmitter class]) {
     RCTAssert(RCTClassOverridesInstanceMethod(self, @selector(supportedEvents)),
               @"You must override the `supportedEvents` method of %@", self);