Revert "Plugins: remove init_qt hook; clean up"

This reverts commit e20369bf94.

gui/qt/__init__.py

@@ -92,6 +92,7 @@ class ElectrumGui:
         self.build_tray_menu()
         self.tray.show()
         self.app.connect(self.app, QtCore.SIGNAL('new_window'), self.start_new_window)
+        run_hook('init_qt', self)
 
     def build_tray_menu(self):
         # Avoid immediate GC of old menu when window closed via its action

gui/qt/main_window.py

@@ -2941,6 +2941,7 @@ class ElectrumWindow(QMainWindow, MessageBoxMixin, PrintError):
             p = plugins.toggle(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.values()):
             name = descr['__name__']