GUI fixes

- do not show command result dialog when result is None
- apply fmtstr, if available

+ fix io import in secop.core
+ change old style <basecls>.__init__(self, ...) calls to super().__init__(...)

Change-Id: I599d5d8e8ff430ea9454a0858d703290e87454fc
Reviewed-on: https://forge.frm2.tum.de/review/c/sine2020/secop/playground/+/26397
Tested-by: Jenkins Automated Tests <pedersen+jenkins@frm2.tum.de>
Reviewed-by: Jens Krueger <jens.krueger@frm2.tum.de>
Reviewed-by: Enrico Faulhaber <enrico.faulhaber@frm2.tum.de>
Reviewed-by: Markus Zolliker <markus.zolliker@psi.ch>

secop/gui/cfg_editor/node_display.py

@@ -26,7 +26,7 @@ from secop.gui.qt import QHBoxLayout, QSizePolicy, QSpacerItem, Qt, QWidget
 
 class NodeDisplay(QWidget):
     def __init__(self, file_path=None, parent=None):
-        QWidget.__init__(self, parent)
+        super().__init__(parent)
         loadUi(self, 'node_display.ui')
         self.saved = bool(file_path)
         self.created = self.tree_widget.set_file(file_path)