Use diskette icon for saving-related actions again.
http://user-prompt.com/about-antiquated-metaphors-in-icons/
This partially reverts commit f76c017c.

Change-Id: Iec9f0f5d6b62556e922f42247d058df817147da6
Reviewed-on: https://gerrit.libreoffice.org/1889Reviewed-by: Petr Mladek <pmladek@suse.cz>
Tested-by: Petr Mladek <pmladek@suse.cz>