Add support for unlaunched private sites

[scruffian]

This PR lays the groundwork necessary for the "private by default" project. It works in combination with this server side patch: D19586-code.

There are more changes necessary to make it possible to launch the site from Calypso, but I wanted to keep this PR small.

Changes proposed in this Pull Request

• Sites created using the site step are created as Private. They are also set to unlaunched.
• When a user has an unverified email address and an unlaunched site, they are able publish content and import sites but they can't change their privacy settings.

Testing instructions

• Apply this patch to your sandbox: D19586-code.
• Open an incognito window
• Create a new site and account at http://calypso.localhost:3000/start
• Verify that you are not able to publish posts or pages, or import anything but you are able to change your privacy settings
• Verify that you do not see a "launch banner" on the front end of your site
• Create a new site at http://calypso.localhost:3000/start/private
• Verify that you ARE able to publish posts or pages, and import, but you are NOT able to change your privacy settings
• Verify that you DO see a "launch banner" on the front end of your site
• Verify your email address
• Now you should be able to publish content and import on both sites, and change your privacy settings
• You should still see a "launch site" banner on the front of the site created at /start/developer.

[matticbot]

Test live: https://calypso.live/?branch=add/unlaunched-sites

[scruffian]

Might be worth setting a different notice text

[scruffian]

Create private sites as "unlaunched"

[mattwiebe]

TIL Fragment shorthand

[mattwiebe]

The code looks fine and tests properly according to your criteria, but I'm still wondering about the TODOs in a couple of places.

Looks like it's still supposed to get some site launching capability?

[scruffian]

Looks like it's still supposed to get some site launching capability?

Yeah I'll add that in a new PR