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/Views/RCTView.m

@@ -129,6 +129,8 @@ static NSString *RCTRecursiveAccessibilityLabel(UIView *view)
   return self;
 }
 
+RCT_NOT_IMPLEMENTED(-initWithCoder:unused)
+
 - (NSString *)accessibilityLabel
 {
   if (super.accessibilityLabel) {
@@ -236,10 +238,10 @@ static NSString *RCTRecursiveAccessibilityLabel(UIView *view)
 - (void)react_remountAllSubviews
 {
   if (_reactSubviews) {
-    NSInteger index = 0;
+    NSUInteger index = 0;
     for (UIView *view in _reactSubviews) {
       if (view.superview != self) {
-        if (index < [self subviews].count) {
+        if (index < self.subviews.count) {
           [self insertSubview:view atIndex:index];
         } else {
           [self addSubview:view];