Last_changed and last_updated columns on /dev-state page

It would be useful to see when a state has been updated and changed for all entities.
This is useful both for debugging and simply for looking up when something has last happened, e.g. when was the last time the door/window/garage was opened.
Seeing the last update time can also give a hint that a sensor is not working properly if it is not updated for a too long period of time.

super useful!