OSIS-2071  Disable button if the content is not postponable
OSIS-2071  Disable button if the content is not postponable

uclouvain/osis,uclouvain/osis_louvain,uclouvain/osis,uclouvain/OSIS-Louvain,uclouvain/osis_louvain,uclouvain/osis,uclouvain/osis,uclouvain/osis_louvain,uclouvain/OSIS-Louvain,uclouvain/OSIS-Louvain