XMPPStream validatesResponses API

Facebook doesn't respond from the correct JID during negotiation so I making the validation of responses optional for now.
Upgrading GCDAsyncSocket to 7.4 branch, commit 5aa4d2145570ec0cd107e508ca0799b2df0dbabe
Fixing / upgrading Xcode projects
Adding support for SSL pinning. Fixes issue #333
Fixing sample projects to use new TLS certificate evaluation callback style.
Merge branch 'master' of https://github.com/robbiehanson/XMPPFramework