Merge branch 'feature/issue-8680' into v6.3

* feature/issue-8680: (250 commits)
  #8680 Removing unused code
  #8680 Updating Foundation.Nest to determine if it is a menu vs. accordion menu, cleaning scss and updating documentation
  Updating to enhance accessibility
  Updating to enhance accessibility
  #8680 Refactoring Accordion code to use "Tree" related accessibility.
  fix centered columns flowing around uncentered columns
  add row w/ single column to centered-columns visual test
  create visual test for centered columns
  add specificity to centered columns to override :last-child
  Added the Equalizer's dependencies to the config.yml
  Fixed the Equalizer dependencies #8974
  Add check if key exists in map
  Fix ghetto for loop
  Change slides with arrow keys only if the data-accessible option is true
  Correct documentation for tooltip dependency list
  Add is-collapse-child class
  Enable the script to load in DoneJS SSR
  Added background, and color css declarations for table tfoot
  Fixed the Meter black border in Edge
  Fixed the progress-bar black border in IE and Edge
  ...

# Conflicts:
#	scss/grid/_flex-grid.scss