#356 Make a quite empty demo code compile and run (but it does pretty much nothing...).

HappyHeart.xcodeproj/project.pbxproj

XCodeTemplates/Main.xctemplate/___FILEBASENAME___.cpp

XCodeTemplates/Model.xctemplate/___FILEBASENAME___.hpp

src/Problems/Demo/InputParameterList.hpp

src/Problems/Demo/Model.cpp

src/Problems/Demo/Model.hpp

src/Problems/Demo/main.cpp