Add list of bitcoin exchanges by country to help people get bitcoin

[wbnns]

This PR is a work in progress that creates an Exchanges page with a list of exchanges by country, starting with a list of exchanges in the world's 20 largest economies.

Preview:

This page:

• Links to the Find an Exchange button on the Getting Started page and helps many of the new people entering the Bitcoin ecosystem via Bitcoin.org who are looking to adopt the technology, get bitcoin.
• Improves SEO for Bitcoin.org, because the site can now potentially rank very well for "Bitcoin Exchange" as well as longer tail terms that include country names that are contained on the page (i.e. Bitcoin Exchange China, Bitcoin Exchange India, etc.) .
• Has unique anchor links for each country that people can share on social media that will allow others to find the bitcoin exchanges that are available for their specific country.
• Allows us to have an opportunity to focus the wallets page on products that allow people to maintain full control over their funds (Resolving Bitcoin bank listings #1109, because we could move custodial wallets that provide exchange services off of the wallets page to this page).
• Will also be accessible via the Resources dropdown menu.

Unless others object, I will standby this week in case anyone would like to discuss, and plan to finish this, this weekend, and subsequently schedule this to be merged on Wednesday, January 11th.

[JTuwiner]

@wbnns Hey, this looks good :)

If this would replace the link to BBWW on the get started page...Perhaps have a link to BBWW on this page then? I can see in my analytics that people coming from Bitcoin.org are viewing about 3 pages on my site -- so it seems BBWW is providing some useful information to them. Also would be good for people who aren't in any of the 20 countries listed.

I think this page will be good since it simplifies the options, but some of the readers would be missing out not knowing about BBWW and the details it provides about the exchanges. What do you think?

Also, if there is any way I can help you collect data for more exchanges and countries on this page, let me know!

[wbnns]

@JTuwiner Hey, thanks for the kind words and offer to help. Yes, I'm moving the link we had to you, onto the page:

[JTuwiner]

Sweet! I hope enough eyes will see it down there at the bottom of the page ;) I think BBWW is really useful for people, but I'm a bit biased there. Haha!

No problem about the offer to help. It's great to see more updates being made to bitcoin.org -- seems like it was quiet for quite some time. If there's anything I can do to help the site, I'm seriously all ears.