Customizer: Bind `input` and `propertychange` events for range input types.

props voldemortensen, westonruter.
fixes #30223.

git-svn-id: https://develop.svn.wordpress.org/trunk@30219 602fd350-edb4-49c9-b593-d223f7449a82
Twenty Fifteen: Remove a gap between content and footer when the sidebar is longer than the content.

Props iamtakashi, fixes #30228.




git-svn-id: https://develop.svn.wordpress.org/trunk@30220 602fd350-edb4-49c9-b593-d223f7449a82