Renewables with quadratic cost curves: lack of `active_power_limits`

[luke-kiernan]

In order to fix an issue with renewables not having active power bounds, I added a formulation into the quadratic curve objective function file. To keep the ActivePowerVariableLimitsConstraint out of IOM, I'm reverting that. Which means I'm re-introducing this bug. Fix it here in IOM by making a renewable-specific implementation, or find another work-around.