Function addSingleton

extlibs/catch/include/catch/catch.hpp:12957–12959

    ISingleton::~ISingleton() {}

    void addSingleton(ISingleton* singleton ) {
        getSingletons()->push_back( singleton );
    }
    void cleanupSingletons() {
        auto& singletons = getSingletons();
        for( auto singleton : *singletons )