Graphics: add reStrucTured text to degre-structuration

Add reStrucTured at same level as Framemaker.

Signed-off-by: Olivier Carrère <carrereo@gmail.com>
Acked-by: Angela Cristina <acristina@redaction-technique.org>
(cherry picked from commit 50f93f602c0c91fc4ee795a44baedf050e1858d0)
Signed-off-by: Olivier Carrere <carrereo@gmail.com>