Update switch states periodically

[felipecrs]

This was initially discussed here so I decided to create a dedicated issue for it.

In my opinion, it would be great if the switch state would copy the state of their counterpart binary sensors, even if they could be some seconds outdated. I believe this caveat is completely acceptable and worthwhile.

When turning on the switch, assume state is true until the next read. The same for switch.turn_off.