[Private sites] Copy updates

[adamziel]

Changes proposed in this Pull Request

This PR improves the copy related to private sites.

Test instructions and details:

Settings page

With this PR, it should provide an intuitive copy that distinct between the private and coming soon modes.

SEO settings page

Before this PR, it always displays the Coming Soon copy, even if the site is just private:

With this PR it displays appropriate copy:

[matticbot]

Test live: https://calypso.live/?branch=update/private-sites-copy-updates

[matticbot]

Here is how your PR affects size of JS and CSS bundles shipped to the user's browser:

Sections (~542 bytes added 📈 [gzipped])

name                  parsed_size           gzip_size
settings                  +1528 B  (+0.4%)     +330 B  (+0.3%)
themes                     +469 B  (+0.1%)      +53 B  (+0.1%)
settings-performance       +469 B  (+0.2%)      +53 B  (+0.1%)
plugins                    +469 B  (+0.1%)      +53 B  (+0.1%)
hosting                    +469 B  (+0.3%)      +53 B  (+0.1%)

Sections contain code specific for a given set of routes. Is downloaded and parsed only when a particular route is navigated to.

Legend

What is parsed and gzip size?

Parsed Size: Uncompressed size of the JS and CSS files. This much code needs to be parsed and stored in memory.
Gzip Size: Compressed size of the JS and CSS files. This much data needs to be downloaded over network.

Generated by performance advisor bot at iscalypsofastyet.com.

[michaeldcain]

Code-wise, LGTM.

[adamziel]

Test failures look unrelated - merging