- Don't limit controls to show only on horizontal
- This enables controls to show for both horiz and vert
- The vertical CSS specifies a block so will require tweaking
- Filter out space-between from vertical controls

- Adds an additional attribute to showJustifyControls to navigation
block so the Nav Editor screen can hide the controls, since that screen
is intended to create/edit nav menus and not format/style.

- Use 'showJustifyControls' since the positive is easier to reason and
there is already a 'showSubMenuIcon' attribute that also defaults to
true