Purchases: site identification

[p3ob7o]

The list of sites in /purchases is confusing, only the site name is visible, which can be ambiguous as not unique.

We should add the blavatar and URL, like in the site picker.

[fabianapsimoes]

cc @mikeshelton1503

[umurkontaci]

FWIW, we also now have the slug property in purchases list, we might be helpful.

[mikeshelton1503]

Ok so for v1 let's just add the primary url like this:

I'm opting not to include the blavatar for a couple reasons:

1. Not all users have one set so some users would just see the generic blavatar for each site which certainly doesn't help.
2. This would be a change to the section header component that we are using here.

I think work needs to be done on the section header component to address this concern as well as others throughout the UI so keeping that change until v2 will give us time to sort out the best next steps for that component.

[breezyskies]

@mikeshelton1503's design implemented in #2359.