Add ventilation to design heat losses

[jelgerjansen]

Right now the zone model in IDEAS calculates the design heat losses as the sum of transmission heat losses through the wall components, the infiltration losses, and reheating. This issue is to add the design ventilation losses to that calculation.

[jelgerjansen]

A new parameter should be added to the zone model that calculates the ventilation heat losses. I propose to add a default ventilation losses calculation (depending on the nominal ventilation flow rate and the heat recovery rate), which can be overwritten if e.g. the ventilation template (IDEAS.Templates.Interfaces.BaseClasses.VentilationSystem) is used which has a parameter Q_design that represents the ventilation losses in that template.