Clean up the sticky menu and responsive tweaks JS:
- More descriptive names.
- Share cached jQuery elements.
- Fix re-enabling of touch events on the admin menu.
- Fix disabling/enabling of UI Sortable.
Props tollmanz, props sanchothefat, see #26086, fixes #26088.

git-svn-id: https://develop.svn.wordpress.org/trunk@26402 602fd350-edb4-49c9-b593-d223f7449a82