Bug fix: creation of part with no parent created a new parent but didn't
add the part to the parent. 
Adding more unit tests for the Heap and it's notification mechanism.
Again, multiple changes in a commit :-).
1) Removed state type from object instances, not states are always
represented with strings.
2) fixed a number of bugs with tha management of composite instances
3) added lot's of unit tests to composite instance handling
4) preparing for implementation of collections...
Modified OPMObjectInstance to use instance type instead of calculating.