Add cart icon to the list of allowed noticon2gridicons

[justinshreve]

This PR adds the cart icon to the noticon to gridicon transformation list, making it possible to use the cart icon for notifications.

We will be using this for a new order notification for Store on WP.com.

To Test:

• Install notifications-panel per the README.
• Load up this branch.
• Sandbox public-api.
• Open class-notification-builders-v1-1.phpand find the builder for one of the notifications in your stream. For example, build_post_reply for a comment reply.
• Update the set_noticon call to $builder->set_noticon( 'cart' );
• Load up the notifications panel (http://notifications.dev:8888/) and view.
• Verify that you can see the cart icon.
• (You could also load up D7802-code and generate an actual order notification - but I haven't completely written out the testing steps there and they are a bit more involved).

[kwight]

Sweet, looks and works great 👍 I tested by just changing a <Gridicons> icons prop to cart.

[justinshreve]

Thanks for the reviews!

@kwight Just wondering, what is the process for getting changes deployed? Does Lannister handle that? I'm not in a huge rush (I still have some work to do on the .com side) but I wasn't sure if there was anything I needed to do to push it live.

[kwight]

@justinshreve We've just started implementing a two-week rotating schedule for releases (p3fqKv-5V6-p2); I can cut a new beta today, giving us two weeks until production release Nov 8th. Of course, if that doesn't work, just let me know and we'll certainly work something out!

[justinshreve]

@kwight That should work perfectly I think. Thank you!