UI Scaling: Store pre-fiddling default in theme.default_ui_scale

This is in case anything needs to know the ratio between what was the
default and what we then set it to.

EDMarketConnector.py

@@ -1054,6 +1054,7 @@ if __name__ == "__main__":
     if not ui_scaling:
         ui_scaling = '0.0'
         config.set('ui_scaling', ui_scaling)
+    theme.default_ui_scale = root.tk.call('tk', 'scaling')
     if ui_scaling != '0.0':
         root.tk.call('tk', 'scaling', float(ui_scaling))
     app = AppWindow(root)

theme.py

@@ -115,6 +115,7 @@ class _Theme(object):
         self.widgets_pair = []
         self.defaults = {}
         self.current = {}
+        self.default_ui_scale = None  # None == not yet known
 
     def register(self, widget):
         # Note widget and children for later application of a theme. Note if the widget has explicit fg or bg attributes.