Help page improvements

- Only signed-in users can see version information
- Add "Community Edition" text so the header is
  less barren when version information is hidden
- Minor copy edits
- Make all "Quick help" link text the entire body
  of the link. Prior, it wasn't obvious which part
  of each item was an actual link.

Closes #2721 

See merge request !1415

Closes #2585

Closes https://github.com/gitlabhq/gitlabhq/issues/9657

Closes #2702

[ci skip]

[ci skip]

Fix top margin for sign-in button on public pages

Closes #2615

[ci skip]

See merge request !1412

[ci skip]

Closes #2653

Prevent double-prefixing of help page paths

Closes #2679 

See merge request !1400

This was causing the task `gitlab-rake gitlab:incoming_email:check`
to fail.

[ci skip]

8.0.0 is released; add 8.0.1 entry to CHANGELOG

[ci skip]

See merge request !1394

[ci skip]

Add to migration on what to do if you don't want your data.

If you don't want to migrate your CI data , remove the old builds directory.

See merge request !1392

Add to migration on what to do if you don't want your data.

If you don't want to migrate your CI data , remove the old builds directory.

See merge request !1392

Mention Reply by email in installation doc.

Added the "Enable Reply by email" section and moved the others around.

See merge request !1390

Ci migration doc improvements

Use export improvements in CI 8.0.1, make upgrades a more prominent part of the process, do not shut down GitLab during CI data import.

See merge request !1387

Ci migration doc improvements

Use export improvements in CI 8.0.1, make upgrades a more prominent part of the process, do not shut down GitLab during CI data import.

See merge request !1387

documentation on ssl verification in web hooks



See merge request !1386