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/RCTRedBox.m

@@ -90,6 +90,8 @@
   return self;
 }
 
+RCT_NOT_IMPLEMENTED(-initWithCoder:(NSCoder *)aDecoder)
+
 - (void)dealloc
 {
   [[NSNotificationCenter defaultCenter] removeObserver:self];
@@ -145,12 +147,12 @@
 
 #pragma mark - TableView
 
-- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
+- (NSInteger)numberOfSectionsInTableView:(__unused UITableView *)tableView
 {
   return 2;
 }
 
-- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
+- (NSInteger)tableView:(__unused UITableView *)tableView numberOfRowsInSection:(NSInteger)section
 {
   return section == 0 ? 1 : [_lastStackTrace count];
 }