Fix issues with capacity control signals

[jmaguire1]

Users should be able to allow a capacity (and for ASHPs, for the main heat pump AND the backup element) to be passed in directly. However, this isn't working correctly:

• Initialization seems to reflect the control signals being sent, which means starting way off from the setpoint temperature
• While the control signal for the heat pump is used, the backup capacity is not being controlled correctly.

Here's an example where the space starts way outside the setpoint temperature, and the power is basically all the backup element running (because the heat pump is being passed a constant capacity of 20 W):

Currently working on a fix in #212