Safe-react: [Address Book v2] Export the address book

[katspaugh]

When clicking on the Export button (from #2234):

Generate a CSV with three columns:

• name
• address
• chain id

“OpenSea”;”0x12AF43637576573264353453”;"1"
“Vitalik”;”0x3C4B85A093412AF43637576573”;"1"

• Create a file blob and a link for it:

        const blob = new Blob([CSV], {type: "octet/stream"}),
        const url = window.URL.createObjectURL(blob);
        a.href = url;
        a.download = fileName;

• Show the link in a modal window (design tbd in #2233)

[KristinaMayman]

I think we should specify that what is going to be exported is a CSV, probably in the modal.

[alongoni]

Here is the design for the AB v2 Export flow (first approach). Suggestions are appreciated :)

https://www.figma.com/proto/txqgq1QhrFFe2NlwPRh0bz/Gnosis-Safe-Web---2021-02-05?node-id=201%3A43777&viewport=240%2C310%2C0.42349866032600403&scaling=min-zoom&page-id=3%3A43299%3Ffuid%3D789860674698606135%3Ffuid%3D789860674698606135

cc @KristinaMayman

[katspaugh]

Really nice, @alongoni!
I've left feedback in #2233. Let's discuss the designs there.