Split test main navigation changes

[manospsyx]

One of the earliest tweaks we did to boost merchant activation on Woo Express / the Ecommerce Plan was to deliver a more selling/commerce-optimized navigation. We have:

• reduced the number of "Homes" on WP.com from three to two (!);
• flattened important Woo areas (Orders, Customers) into the main menu;
• re-purposed the existing WooCommerce submenu to contain submenu items previously added by Extensions under the WooCommerce submenu -- a practice that contributed to bloat and made important flows difficult to discover.

This work is still incomplete, as Woo Settings are still missing-in-action in the Settings submenu, which is still emphasizing the publishing capabilities of WordPress and WP.com.

After completing this work, we should run an experiment to compare how the two approaches affect merchant activation and discuss the results.