Improvements to UX flow.

* Remember the state of the "add to shop" checkbox when adding an item
* Made shop blocks collapsible in the shopping list view
* Bulk actions (delete or add to shopping list) on the screen
  for editing items in a shop
* Preference to drop ticked items to the bottom of the list, and bulk
  unchecking of items on the shopping list.  This provides an alternate
  workflow to deleting and re-adding the items, if desired.
* Scroll each newly added item into view
* Import and export functionality for data in JSON format
* About screen displaying version number
