Other way of setting heating/cooling load

[wouterpeere]

Currently, it is in the gui only possible to put in energy loads in kWh. However, sometimes, it is possible to have a fixed profile and just a difference in yearly energy demand. In this issue the possibility is investigated to include a second way to input the monthly energy loads based on a monthly load percentage and a yearly energy demand.

• Create relative class in Load Classes
• Create tests for relative heating/cooling input
• Create documentation for relative heating/cooling input
• Add relative class to GUI

[wouterpeere]

This will be implemented after issue wouterpeere/GHEtool#45 is finished

[wouterpeere]

Also to be implemented here: seperate DHW and SPF for heating/cooling/DHW.