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.

Examples/UIExplorer/UIExplorer.xcodeproj/xcshareddata/xcschemes/UIExplorer.xcscheme

@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <Scheme
-   LastUpgradeVersion = "0630"
+   LastUpgradeVersion = "0700"
    version = "1.3">
    <BuildAction
       parallelizeBuildables = "YES"
@@ -86,6 +86,8 @@
             ReferencedContainer = "container:UIExplorer.xcodeproj">
          </BuildableReference>
       </MacroExpansion>
+      <AdditionalOptions>
+      </AdditionalOptions>
    </TestAction>
    <LaunchAction
       selectedDebuggerIdentifier = "Xcode.DebuggerFoundation.Debugger.LLDB"
@@ -95,6 +97,7 @@
       buildConfiguration = "Debug"
       ignoresPersistentStateOnLaunch = "NO"
       debugDocumentVersioning = "YES"
+      debugServiceExtension = "internal"
       allowLocationSimulation = "YES">
       <BuildableProductRunnable
          runnableDebuggingMode = "0">