anges in LimitCalculator and HypoTestCalculator classes: usage of ModelConfig class</h4>

<ul>
<li>
The RooStats calculator interfaces have been changed to use the <tt>ModelConfig</tt> class.
All the setter methods with the parameter lists, pdf instances and name have been removed from the interfaces.
The <tt>SetWorkspace(RooWorkspace &amp; )</tt> has also been removed, while a <tt>SetModel(const ModelConfig &amp;)</tt>
function is introduced.
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  </li>
  <li>
Users are supposed to pass all the model in