Wp-calypso: Sidebar: add 'view cart' link to sidebar

[rickybanister]

If a customer has a plan in their cart, but they haven't checked out, we display a global notice to them on page load. I believe this fades away after a short time.

In addition to that we should add a pervasive link to the sidebar inviting them to view cart:

That was a quick inspector hack and it could use design, but this would be a nice improvement.

[davemart-in]

@lcollette I think this is a good idea. Once y'all are happy with the direction of the design, if you need engineering help to implement this, please re-add it to the Manage Group Backlog project. Thanks!

[lcollette]

Roger that, @davemart-in!

[LauraSWP]

I really like this idea!

[fditrapani]

I just wanted to highlight an alternative solution we've implemented on the domain screen and that I shared with Rick as well. The idea would be to show a cart button in the page header if there's something in the cart and would save us from adding another link to the sidebar:

[rickybanister]

I'm not sure the page header feels appropriately 'global' to the site. That's why I chose the sidebar, there felt like some amount of context or relationship by putting it next to the Plan tab. Almost like a red dot, but actionable and labeled.

I think it would make sense to have other indications that you've left something in your cart on related screens (like if there's a domain in cart and you're thinking about domains, that makes sense), but I'd like for us to think through the overall anatomy of our screens and header area before committing to this. We aren't consistently using that area for primary actions yet, for instance.

Let's keep thinking it through. cc @lcollette