EclipseState: make it instantiable without a grid

instead of throwing, we now add a warning to the parser log...

there are plenty of places where an EclipseState object is useful without a grid, e.g. most of the unit tests would not need to add a "dummy grid" to their decks anymore...
yes: It used to be avoiding circular pointers. but come think about it, I can also use a `shared_ptr`, because I initially tried to use an `EclipseState` pointer but that failed because EclipseState is not yet fully defined here and cannot be because it requires the `GridProperties` class. Also note that this can be a NULL pointer. As you can see this is a serving of spaghetti code with a healthy sauce of side constraints ;)

I changed the pointer in the current version, thanks..