glTF: allow to move camera also by keyboard in orbit mode.

Change-Id: Ibf16b9651988358c30d649dd937813329d0f64ec
(cherry picked from commit 9e8dbd37c4dda5d07c22c66a5a2b08cce4d175f5)
Reviewed-on: https://gerrit.libreoffice.org/10368
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>