Fix for issue #398, AdminUI: Recalculate total after delete

Not sure if anyone was working #398, but it had been bugging me for a while.

This PR makes the following behavioral changes:

1. Deleting the last item removes the `item-list` table, `pagination` and `header` and displays "No 'list-name' found"
2. Deleting an item from the last page (or the first and only page) updates `header` and `pagination`
3. Deleting an item when not on the last page fetches the next item (to fill the max with `maxItems`) and updates the `header` and `pagination`
4. Deleting the last remaining item on the last page (when there are multiple pages) redirects to the previous page

I also refactored some code to make it reusable.

1. The `getPages` method in `lib/list.js` (which I reuse to updated `pagination`)
2. A `rows` mixin (which I use reuse after fetching the next item to fill a page)
3. A `pagination` mixin (which I also use to update `pagination`)