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

Add missing rake and change nginx config for CI migration

/cc @marin

See merge request !1385

Fix CI permissions

![Screen_Shot_2015-09-21_at_20.23.16](https://gitlab.com/gitlab-org/gitlab-ce/uploads/6f40699507d0dce148d0054a093f0d63/Screen_Shot_2015-09-21_at_20.23.16.png)

This fixes two problems:
- Allow developers to retry builds
- Hide advanced project options from CI page for non-admin users

See merge request !1379

Fix CI permissions

![Screen_Shot_2015-09-21_at_20.23.16](https://gitlab.com/gitlab-org/gitlab-ce/uploads/6f40699507d0dce148d0054a093f0d63/Screen_Shot_2015-09-21_at_20.23.16.png)

This fixes two problems:
- Allow developers to retry builds
- Hide advanced project options from CI page for non-admin users



See merge request !1379

Add missing rake and change nginx config for CI migration

/cc @marin

See merge request !1385

Reformat and copy edit the CI-to-CE migration guide

[ci skip]

See merge request !1335

[ci skip]

Tweak remaining CSS for Markdown preview

See merge request !1383

- Rename "Finishing Up" to "Nginx configuration"
- Add fourth "Finishing Up" section
- Add Troubleshooting section with a link to backup restoration docs
- Change a few indented blocks into fenced blocks so they're highlighted
  properly.
- Added Marin's suggestions for CI-to-CE-on-different-server section.