Cache sustainability_share separate from dataset value
Cache sustainability_share separate from dataset value

Caching the sustainability_share would bypass the correct calculation of
sustainable_factor in cases where the share is calculated first. This
could result in negative primary demand of fossil in the case of primary
demand nodes with non-zero loss.

Closes quintel/etsource#1665

quintel/etengine,quintel/etengine,quintel/etengine,quintel/etengine