Disentangle plugins and window management; use Qt signals

gui/qt/main_window.py

@@ -565,8 +565,6 @@ class ElectrumWindow(QMainWindow, PrintError):
 
     def update_wallet(self):
         self.update_status()
-        if self.wallet is None:
-            return
         if self.wallet.up_to_date or not self.network or not self.network.is_connected():
             self.update_tabs()
 
@@ -2868,6 +2866,7 @@ class ElectrumWindow(QMainWindow, PrintError):
             p = plugins.toggle_enabled(self.config, name)
             cb.setChecked(bool(p))
             enable_settings_widget(p, name, i)
+            run_hook('init_qt', self.gui_object)
 
         for i, descr in enumerate(plugins.descriptions):
             name = descr['name']