v0.19.0

Improvements

• #member_actions and #collection_actions can return an array of things that
  respond to #to_partial_path, including but not limited to Links.
• Partials can be ordered
• Added a batch actions feature
• Frontend assets can be set up via yarn add @superadministration/super
• Added a button to export to CSV

Breaking changes

• The Link object can now only be rendered via #to_partial_path instead
  of through #to_s.
• Super::Layout doesn't render arrays of partials