Properly set-up control references

[rodrigomha]

Currently control references from Power and Voltage are directly taken from the output of the PowerFlow. For example:

• Control_ref[P_ref] = get_activepower(PF)
• Control_ref[V_ref] = get_busvoltage(PF)

The set-up of control references should update those values, depending on specific components connected in each device, such that P_ref and V_ref match the solution obtained from the PF. That is, follow Milano's implementation of such parameters.