Made the following changes:
  - Added cocoon and jquery-turbolinks into the gemfile so we could use javascript for the edit page
  - Updated the Packlist model to include the accepted-nested-attributes for items
  - Modified the packlists controller update method to accept the editing of items.
  - Included the cocoon and jquery-turbolinks in the aplication.js file
  - Created an item-fields partial and added the code so a user can edit the items when going to the
     edit page.
  - Put the code in for the edit view so users can add or remove items and change quantities