Modular energy_source for entities

[wasmoo]

I'd like to recreate every entity with each energy source. Here are the ones I've had to hack:

• solar panels

• roboport

• beacon

• electric-turret

My current hack is to create an invisible generator and electric-pole on the same spot, but certain behaviors still don't work correctly, like the UI or fast-transfer.

As an aside, it would be nice if `generator`, `burner-generator`, and `reactor` had similar prototypes so it would be easier to convert between them.