Remove 'native data' and 'native units' (#331)

Resolves #331 (closed)

Somehow resolves #850 (closed)

GUI/Model/Job/JobItem.cpp

@@ -310,6 +310,9 @@ DataItem* JobItem::createDiffDataItem()
     if (auto* spec_diff = dynamic_cast<Data1DItem*>(diffDataItem()))
         spec_diff->setDiffPlotStyle();
 
+    if (auto* intensity_diff = dynamic_cast<Data2DItem*>(diffDataItem()))
+        intensity_diff->setCurrentGradient(m_realItem->data2DItem()->currentGradient());
+
     return m_diffDataItem.get();
 }
 
@@ -338,6 +341,10 @@ void JobItem::copyDatafileItemIntoJob(const DatafileItem* srcDatafileItem)
         Frame frame = instrumentItem()->makeFrame();
         m_realItem->data1DItem()->setDatafield(
             {frame.clone(), old->flatVector(), old->errorSigmas()});
+    } else if (rank() == 2) {
+        // use color scheme from loaded data
+        ASSERT(data2DItem());
+        data2DItem()->setCurrentGradient(m_realItem->data2DItem()->currentGradient());
     }
 }
 
@@ -585,11 +592,6 @@ void JobItem::readFrom(QXmlStreamReader* r)
             createDatafileItem();
             m_realItem->readFrom(r);
             createDiffDataItem()->checkXYranges(m_realItem->dataItem());
-
-            if (rank() == 2)
-                dynamic_cast<Data2DItem*>(diffDataItem())
-                    ->setCurrentGradient(m_realItem->data2DItem()->currentGradient());
-
             importMasksFromDatafileItem();
             XML::gotoEndElementOfTag(r, tag);