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
Add support for Google OAuth2
Merge pull request #294 from ChatSecure/X-OAuth2-Google

Add support for Google OAuth2
NSXMLElement attributeBoolValueForName now supports @"true" and @"false"
XMPPMessageArchiving xmppMessageArchivingStorage Property

Fixes #295
Missing Returns
XMPPCoreDataStorage autoRemovePreviousDatabaseFile API
XMPPRoster autoClearAllUsersAndResources API

Fixes #238
Fixes an Issue where deleting a resource wouldn't update a User's primary resource
XMPPAutoTime APIs
XMPPCoreDataStorage APIs

addWillSaveManagedObjectContextBlock:
addDidSaveManagedObjectContextBlock:
XMPPvCardTempModule dispatch_async where appropriate

Fixes #302
Roster is only accepted if it has been asked for

Relates too #300
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