added contextual privateCreators dico to ParsedDicomFile -> this allows you not to have to define a DefaultPrivateCreator. This was tested only in the scope of C-Find requests but should not have impact on other parts since it is not used out of C-Find right now

More contributed samples of plugins can be found and added in
the "OrthancContributed" repository on GitHub:
https://github.com/jodogne/OrthancContributed/tree/master/Plugins