Extend component realize methods and addreses #184

Can now invoke realization to computational stage through Component's public (non-virtual) interface.
Virtual realize methods renamed to `extendRealize<...>()`.
Realization occurs with the System the component was added to.  If system reference is empty, you also now get a (hopefully) meaningful message.
I am happy to remove these from Component.

I vaguely remember arguing not to expose the system realize methods at all. I believe I was overruled. There was an agreement to add them to Model, but I don't think Model should be treated as anything special especially when we want to move toward aggregates of models in which case a Model is just like any other component.

I agree that if `realize()` is exposed it should be on the thing that holds the system. That is currently model, but that should change. Perhaps we need to invent the Study to at least be the holder/owner of the system. Then system level operations like realize make sense.