Added trove backup via horizon

The trove chapter in the user guide did not have
a section on how to use horizon to backup
and restore a database instance.

This commit covers how to backup and restore
a db instance using horizon.

This commit is a partial implementation of the
blueprint.

Change-Id: Iceb7a2e62c633d6f59d9d89aa6ae8ce30e354068
blueprint: user-guide-trove-chapter
Add index pages for Chinese and Korean documents.

Modified the header of draft-i18n-manuals.html,
removed Chinese and Korean entries from draft-i18n-manuals.html.

Add Chinese and Korean entries to dropdown_releases_and_languages.tmpl.

Change-Id: I39111882fc4f3cdf2d01df451b02bd824ef9967c
Merge "Added trove backup via horizon"
Merge "Add index pages for Chinese and Korean documents."