Fixed: main menus were too far apart

Previously the main menus were farther apart than the Aristo 2 PSD indicated, and too far apart visually.

This commit reduces the horizontal margin between menu items that have originated from Interface Builder. A value of 9.0 for horizontal margin (down from 12.0) reduces the margin on both sides of the menu by 3px, reducing the inter-menu spacing by a total of 6px.

Fixes #1809