Start rearranging the docs for a utilities update

— Rename display docs page
— Move print display utils to display utils page
— Drop remaining of responsive utils page as it's being replaced with display utils
— Update nav to reflect changes

docs/layout/utilities-for-layout.md

@@ -0,0 +1,21 @@
+---
+layout: docs
+title: Utilities for layout
+description: Use any of our dozens of responsive utility classes for showing, hiding, aligning, and spacing content.
+group: layout
+---
+
+For faster mobile-friendly and responsive development, Bootstrap includes dozens of utility classes for showing, hiding, aligning, and spacing content. Below is a primer on what's included in Bootstrap and how these utilities can help you with layout.
+
+## Contents
+
+* Will be replaced with the ToC, excluding the "Contents" header
+{:toc}
+
+## Changing `display`
+
+## Flexbox options
+
+## Margin and padding
+
+## Toggle `visibility`