Fix loading bookmarks pages past the first.

I was messing with the wrong managed object contexts in a couple places.

Bonus:

* Stop contortions to reach ivar, just use a hidden property.
* Delete unused back item code in bookmarks list.
* Delete pointless table view begin/endUpdates in bookmarks list.
Hide/show avatar atop basement as appropriate.

* If the setting is turned off.
* If the logged-in user does not have an avatar. (And don't crash here either.)