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/base.py

@@ -8,6 +8,7 @@
 
 from hscommon.notify import Listener
 
+
 class DupeGuruGUIObject(Listener):
     def __init__(self, app):
         Listener.__init__(self, app)
@@ -27,4 +28,3 @@ class DupeGuruGUIObject(Listener):
 
     def results_changed_but_keep_selection(self):
         pass
-