Squashed 'includes/menu-item-custom-fields/' content from commit 963bc54

git-subtree-dir: includes/menu-item-custom-fields
git-subtree-split: 963bc542a895dae4bf9e92c5dd0e11d2a70e5b9f
Merge commit '234bd3dfe59b7828dfaba10683b9f9f3c537719c' as 'includes/menu-item-custom-fields'