Increased warning levels to -Wall -Wextra, and fixed Xcode 7 beta issues

Summary:
@public

I've increased the warning levels in the OSS frameworks, which caught a bunch of minor issues. I also fixed some new errors in Xcode 7 relating to designated initializers and TLS security.

Test Plan:
* Test the sample apps and make sure they still work.
* Run tests.

React/Base/RCTTouchHandler.m

@@ -40,12 +40,11 @@
 
 - (instancetype)initWithBridge:(RCTBridge *)bridge
 {
+  RCTAssertParam(bridge);
+
   if ((self = [super initWithTarget:nil action:NULL])) {
 
-    RCTAssert(bridge != nil, @"Expect an event dispatcher");
-
     _bridge = bridge;
-
     _nativeTouches = [[NSMutableOrderedSet alloc] init];
     _reactTouches = [[NSMutableArray alloc] init];
     _touchViews = [[NSMutableArray alloc] init];
@@ -58,6 +57,8 @@
   return self;
 }
 
+RCT_NOT_IMPLEMENTED(-initWithTarget:(id)target action:(SEL)action)
+
 typedef NS_ENUM(NSInteger, RCTTouchEventType) {
   RCTTouchEventTypeStart,
   RCTTouchEventTypeMove,
@@ -163,7 +164,7 @@ RCT_IMPORT_METHOD(RCTEventEmitter, receiveTouches);
  */
 - (void)_updateAndDispatchTouches:(NSSet *)touches
                         eventName:(NSString *)eventName
-                  originatingTime:(CFTimeInterval)originatingTime
+                  originatingTime:(__unused CFTimeInterval)originatingTime
 {
   // Update touches
   NSMutableArray *changedIndexes = [[NSMutableArray alloc] init];
@@ -269,12 +270,12 @@ static BOOL RCTAnyTouchesChanged(NSSet *touches)
   }
 }
 
-- (BOOL)canPreventGestureRecognizer:(UIGestureRecognizer *)preventedGestureRecognizer
+- (BOOL)canPreventGestureRecognizer:(__unused UIGestureRecognizer *)preventedGestureRecognizer
 {
   return NO;
 }
 
-- (BOOL)canBePreventedByGestureRecognizer:(UIGestureRecognizer *)preventingGestureRecognizer
+- (BOOL)canBePreventedByGestureRecognizer:(__unused UIGestureRecognizer *)preventingGestureRecognizer
 {
   return NO;
 }