Menu Items Using Live Link

[MatthewKennedy]

This PR uses live links rather than paths stored in the database and are both accessible through the standard Storefront and API.

Benefits:

• Paths are not stored in the DB, so no chance of data ever being out of sync due to some unforeseen circumstance such as a dev changing the Spree::Config[:storefront_product_path] at some stage after menus have been created.

Downside:

• Performance may be slower as links are loaded live, but the cache might resolve this.

NOTE:
Spree::Config[:storefront_product_path] has been added to the Front End config/roots.rb allowing users to set the frontend taxon and product paths, helping users migrate from other platforms to Spree and keep their paths example:
/collections/women vs /t/women.

[damianlegawiec]

Nice!