Add forgotten print command `plot3` to octavebackend print commands.

Authored by sirgienko on Apr 7 2018, 4:25 PM.

Description

Add forgotten print command plot3 to octavebackend print commands.

Summary: This command missing, so cantor don't show plot result of this command. This change fix it.

Reviewers: Cantor, asemke

Subscribers: Cantor, KDE Edu

Tags: KDE Edu, Cantor

Differential Revision: https://phabricator.kde.org/D12022