XEP-0191 (blocking)

Adding implementation of XEP-0191 (blocking) based on implementation of
XEP-0016 (privacy)

This extension can do :
- Block jid
- Unblock jid
- Unblock all
- Get blocking list
Code consistency with the rest of project

Replacing NSString by XMPPJID
Merge pull request #289 from phetsana/XEP-0191

XEP-0191: Blocking Command
Update README.markdown
Fix for XEP 191: Unblock not handled correctly

Fixes #311
Validating Info/Query (IQ) stanzas in the Extensible Messaging and Presence Protocol (XMPP)

Fixes #300
NSXMLElement Convenience methods for Creating elements.
Don't use NSXMLElement description
RootViewController Title Label is now Visible on iOS 7
Merge branch 'master' of https://github.com/robbiehanson/XMPPFramework
XEP-0307