Add picture_on/pictures_on/picture_off/pictures_off to ElectricEnergyInterface

[Deadlock989]

I've been messing around with lamps because I need an entity which:

(a) Requires electricity to work
(b) Displays an overlay sprite when receiving electricity

But I also need to change that overlay sprite. So the current version of what I'm trying to do has to proliferate copies of the lamp entity with different picture_on sprites. This means they all show as separate power consumers in the power stats flow.

What I need is an entity which is half-lamp, half-SimpleEntityWithForce. If ElectricEnergyInterface displayed an overlay when it was powered the way lamps do, it would fit that bill perfectly.

Use case: a sign-like entity which displays an overlay, which can be changed from variant to variant with run-time scripting, and only displays it when powered. An electric sign with a selection GUI, basically.