Feature/class basedview

```python
#Check whether user loged in
            if users.get_current_user():
                #Create link logout & text
                url = users.create_logout_url(request.get_full_path())
                url_linktext = 'Logout'
            #Else
            else:
                #Create link login & text
                url = users.create_login_url(request.get_full_path())
                url_linktext = 'Login'
            #context variables:
            kwargs['greetings'] = greetings
            kwargs['guestbook_name'] = guestbook_name
            kwargs['url'] = url
            kwargs['url_linktext']=url_linktext
```
hãy tách ra khỏi get, để trong self.get_context_data(**kwargs)