Invoice - Allow user to choose what columns display for Invoice lines

Purpose: Limit the number of columns displayed in the borderline table area to make it easier to scroll through invoice lines and identify discrepancies

User story statement(s):

As a acquisitions librarian,
I want to focus the columns displayed in invoice lines table
so that depending on the type of invoice I'm working with I can make better use of the vertical width of the page

Scenarios:

1. Scenario:
   • Given user is viewing an invoice with one or more invoice lines
   • When viewing the table in the invoice lines accordion
   • Then buttons are replaced by a single action menu
2. Scenario: 
   • Given user is viewing an invoice with one or more invoice lines
   • When viewing the action menu for POL
   • Then options include Add, New
   • AND show columns selection
3. Scenario: 
   • Given user has revealed "Show columns" list in action menu
   • When user unchecks a box for a column element
   • Then that element no longer appears as a column in the table
4. Scenario: 
   • Given user has revealed "Show columns" list in action menu
   • When user checks a box for a column element
   • Then that element once again appears as a column in the table