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/miniplot.py

@@ -160,7 +160,7 @@ class MiniPlotFitCurve(MiniPlotCurve):
         return float('-inf')
 
     def __init__(self, formula, params):
-        super(MiniPlotFitCurve, self).__init__()
+        super().__init__()
         self.formula = formula
         self.params = params
 
@@ -193,7 +193,7 @@ class MiniPlot(QWidget):
     autoticky = True
 
     def __init__(self, parent=None):
-        QWidget.__init__(self, parent)
+        super().__init__(parent)
         self.xmin = self.xmax = None
         self.ymin = self.ymax = None
         self.curves = []