Don't override Awful Browser's restored state.

We try to load the URL given to the Awful Browser when appropriate. Restoring
state is not an appropriate time.
Remove unused -themeCell:... methods.

Once upon a time we tried to handle theme changes in table/collection views by
updating each cell. It's much easier to simply reload the table/collection
view, which we've been doing for awhile. These -themeCell:atIndexPath: and
-themeCell:withObject: methods are the last vestiges of this bygone approach,
and they serve only to confuse, so they're gone.