Revision 420 open for discussion

I have made a few changes to Oatc_Dev_2_0\OpenMI.Standard, mainly concerning
the input/output exchange items and the data operations, including their
update calls and values-getters. I briefly discussed a few things with Gena,
but no real details yet. Next week we will work on it together.

The main changes are:
- Item, InputItem and OutputItem are gone, and are replaced by an
ExchangeItem, with a role.
- The DataOperation extends the ExchangeItem (role is then output).
  (please have a look at the DataOperation's comment to see why
   in my view this makes sense)

To form an opinion about it, please have a detailed look at
    NUnitUseCases\CreateCompositionTest.cs
There are four methods:
1. Creating a 'chain' of data-operations.
2. The calibration example that we discussed at the last meeting.
3. The 'connecting 2 components' example that we already had in earlier
    examples.
4. A look inside a LC's Update function, i.e. how it could be implemented
   (comparible to the 'smart wrapper').
Both 2. and 3. use 1. to establish the 'link'.

I didn't find time yet to create and/or update sequence diagrams, class
diagrams, etc., but hopefully the ideas become clear from the example code.

If you think this might be a step in the right direction (i.e. at least not
in the wrong direction), my next action will be to investigate what to do
make the SDK and the GUI up and running again.

Please let me know what you think.

Best regards,
Stef.