Merge pull request #7 from arnoutaertgeerts/DistrictHeating

New GenericModulatingProduction model + improved test setup
Update plugflow test setup to include heat losses
Merge pull request #8 from arnoutaertgeerts/DistrictHeating

Generic Production fix + some updated icons and restructuring
Merge branch 'DistrictHeating' of https://github.com/glennreynders/IDEAS into DistrictHeating
Added insulated pipe model which uses parameters /meter