This patch extends commit 1a47ae24712377821994c3b0309b9437da129d73 and
addresses the following issues:

1. The state of the menu action checkbox was not updated when the other window changed the its state
2. There should be no access to KisConfig in the OpenGL rendering loop (it is slow due to possible disk access).
3. A canvas update call should be issued right after the config changed, otherwise the old state of the grid will be visible until one hovers the canvas

BUG: 389033

1. Open multiple Krita windows and zoom both of them to 1000%
2. Change View->Show Pixel Grid in one of the windows
3. The state on the checkbox and the canvas should automatically update in the other window