[Demo] Add demo app to Liquid Project

Signed-off-by: Miguel M. Almeida <miguelcma@gmail.com>
[Notifications] New notification when user is identified

* Added a new `NSNotification` that is broadcasted when a user is identified: `LQDidIdentifyUser`
* Added a new delegate method that is called when a user is identified: `liquidDidIdentifyUserWithIdentifier:`

Signed-off-by: Miguel M. Almeida <miguelcma@gmail.com>
[Demo] Add a button with an anonymous user

Signed-off-by: Miguel M. Almeida <miguelcma@gmail.com>
[Demo] Add Liquid NSNotification examples to demo app

Signed-off-by: Miguel M. Almeida <miguelcma@gmail.com>