Format files with black

- Format all files with black
- Update tox.ini flake8 arguments to be compatible
- Add black to requirements-extra.txt
- Reduce ignored flake8 rules and fix a few violations

core/gui/stats_label.py

@@ -1,21 +1,23 @@
 # Created By: Virgil Dupras
 # Created On: 2010-02-11
 # Copyright 2015 Hardcoded Software (http://www.hardcoded.net)
-# 
-# This software is licensed under the "GPLv3" License as described in the "LICENSE" file, 
-# which should be included with this package. The terms are also available at 
+#
+# This software is licensed under the "GPLv3" License as described in the "LICENSE" file,
+# which should be included with this package. The terms are also available at
 # http://www.gnu.org/licenses/gpl-3.0.html
 
 from .base import DupeGuruGUIObject
 
+
 class StatsLabel(DupeGuruGUIObject):
     def _view_updated(self):
         self.view.refresh()
-    
+
     @property
     def display(self):
         return self.app.stat_line
-    
+
     def results_changed(self):
         self.view.refresh()
+
     marking_changed = results_changed