f54de8eafb
this makes it possible to define more complicated initializers for grid properties. (needed for example for keywords like ISGU.) This patch does not introduce them yet, but only adds the necessary infrastructure. notes: - to get around cyclic definitions in template classes, the EclipseState is changed to a (defaulted) template parameter which causes the compiler to only look up the class definition at instantiation time. - using std::shared_ptr in the property initializers would lead to cyclic references which would cause memory leaks. To avoid that, plain old references where used in most places. I think this is okay as the GridProperty objects should be considered internal to EclipseState and thus the EclipseState object should live at least as long as GridProperty objects...