set histogram by default for volumes.

close #678

tomwer/gui/reconstruction/nabu/volume.py

@@ -210,6 +210,7 @@ class NabuVolumeWidget(_NabuStageConfigBase, qt.QWidget):
         self.layout().addWidget(spacer, 99, 0, 1, 1)
 
         # set up
+        self._histogramCB.setChecked(True)
         self._spbGPUFract.setValue(90)
         self._spbCPUFract.setValue(90)
         self._usePhaseQCB.setChecked(True)