Enhances SalesApp.Show pages

* When a user clicks to add Purchase to Customer, a Sale entity is
  created and the user is routed to SalesApp.Show
* SalesApp.Show views now separate a Sale from its LineItems
* SalesApp.Show.Layout includes a region where a form for a new LineItem
  will be displayed once a user clicks on + Item button.
Removes uneeded SalesApp.Edit module