System tray menu: Add action to restart calibre. Fixes #2087754 [[Enh…

…ancement] Add 'Restart' to tray menu](https://bugs.launchpad.net/calibre/+bug/2087754)

src/calibre/gui2/ui.py

@@ -288,6 +288,7 @@ def initialize(self, library_path, db, actions, show_gui=True):
                 QIcon.ic('eject.png'), _('&Eject connected device'))
         self.eject_action.setEnabled(False)
         self.addAction(self.quit_action)
+        self.system_tray_menu.addAction(self.iactions['Restart'].menuless_qaction)
         self.system_tray_menu.addAction(self.quit_action)
         self.keyboard.register_shortcut('quit calibre', _('Quit calibre'),
                 default_keys=('Ctrl+Q',), action=self.quit_action)
@@ -1177,6 +1178,9 @@ def write_settings(self):
             self.save_layout_state()
             self.tb_widget.save_state()
 
+    def restart(self):
+        self.quit(restart=True)
+
     def quit(self, checked=True, restart=False, debug_on_restart=False,
             confirm_quit=True, no_plugins_on_restart=False):
         if self.shutting_down: