Chapter 8 fixes

Here's the list of changes:
* In ```8.3```, the note says ```...., you much synchronize...``` whereas it should say ```..., you must synchronize...```
* Fixed the fields attributes of the ```Meta``` classes for ```UserForm```and ```UserProfile``` so that they use tuples instead of lists. This really is not a big deal but did this for consistency with the earlier chapters where we used a tuple for the same attribute in PageForm.
* Removed the extra space from the anchor tag in ```8.4.3```
* Removed the ```context``` variable from the ```user_logout``` view as we did nothing at all with it there.