config: no longer singleton. it is passed to Wallet.__init__

The few other cases that used SimpleConfig.get_instance() now
either get passed a config instance, or they try to get a reference
to something else that has a reference to a config.
(see lnsweep, qt/qrcodewidget, qt/qrtextedit)

electrum/gui/qt/qrtextedit.py

@@ -4,7 +4,7 @@ from electrum.i18n import _
 from electrum.plugin import run_hook
 from electrum.simple_config import SimpleConfig
 
-from .util import ButtonsTextEdit, MessageBoxMixin, ColorScheme
+from .util import ButtonsTextEdit, MessageBoxMixin, ColorScheme, get_parent_main_window
 
 
 class ShowQRTextEdit(ButtonsTextEdit):
@@ -23,7 +23,7 @@ class ShowQRTextEdit(ButtonsTextEdit):
             s = str(self.toPlainText())
         except:
             s = self.toPlainText()
-        QRDialog(s).exec_()
+        QRDialog(s, parent=self).exec_()
 
     def contextMenuEvent(self, e):
         m = self.createStandardContextMenu()
@@ -56,8 +56,11 @@ class ScanQRTextEdit(ButtonsTextEdit, MessageBoxMixin):
 
     def qr_input(self):
         from electrum import qrscanner
+        main_window = get_parent_main_window(self)
+        assert main_window
+        config = main_window.config
         try:
-            data = qrscanner.scan_barcode(SimpleConfig.get_instance().get_video_device())
+            data = qrscanner.scan_barcode(config.get_video_device())
         except BaseException as e:
             self.show_error(repr(e))
             data = ''