Refactor model: JobItem

In this MR the interface of the job item has been overhauled to disencourage the use of the string based interface.

GUI/Models/JobItem.cpp

@@ -239,6 +239,11 @@ InstrumentItem* JobItem::instrumentItem()
     return dynamic_cast<InstrumentItem*>(getItem(T_INSTRUMENT));
 }
 
+InstrumentItem* JobItem::copyInstrumentIntoJob(const InstrumentItem* instrument)
+{
+    return model()->copyItem(instrument, this, T_INSTRUMENT);
+}
+
 void JobItem::setResults(const ISimulation* simulation)
 {
     JobItemUtils::setResults(dataItem(), simulation);