Distributes WP attributes over two tables
Makes helper methods private
Introduces empty tag for (non-)impaired users
Renames variable
Adds changelog entry
Renders empty element tag from view
Uses refactored empty element tag implementation
Distributes work package attributes evenly
Handles empty hook results
Concatenate arrays and discard flattening
Shorten memoization in accessibility helper
Compactify work package attribute list array (fixes integration test)
Split up work package attributes helper method by responsibility
Merge pull request #802 from opf/fix/accessibility_work_package_attribute_list_2258

[FIX] Accessibility work package attribute list 2258