Small update to power production assets

A few updates to power production assets:

• Equipment health now affects assets. For diesel, a decrease in health decreases fuel efficiency. For all other assets, a decrease in health decreases production efficiency. In either case, a typical performance factor curve is applied in determining performance decrease as a function of health.
• Renewable assets can now be shut off between rounds (less mashing [E]).
• When renewable assets are shut off, they suffer no health degradation and incur no operation or maintenance costs.

Cheers =)