Add abbility to report train fuel to the circuit network

[bodobram]

TL;DR

Train stations should include a switch to report the trail fuel to the circuit network.

What?

Currently, train stations can be instructed to read the train contents and report it to the circuit network.
However, as far as I have seen, there is no way that their fuel content is also reported to the circuit network.
Please add a switch that does exactly that.

I'm, however, not sure, how to do that exactly. Imagine a train that is fueled with 50 coals and 10 rocket fuel and carries another 200 coals. Simply putting all signals to the circuit network removes the ability to distinguish between load and fuel. Putting the fuel amount on an artificial signal (like F) removes the ability to distinguish between fuels.
For me personally, it would be enough to be able to enable "Report fuel content" and disable "Report train contents".

Why?

Reading train fuel with the circuit network eases the design of (mixed) refuel stations. I especially encountered it when designing a station that should refuel with rocket fuel if available and coal otherwise (so locomotives can contain both). Simply letting an inserter insert the rocket fuel until fully fueled does not work when some coal is left in the locomative that blocks a fuel slot. It does however work when the train was fueled with rocket fuel beforehand. I work around this by implementing a state machine that fully empties the locomotive before refueling back again.

[Muche]

Also see Rail car/locomotive scanners, Detecting Locomotive Fuel Level, Read train contents from locomotive, Train station can also read locomotive contents when 'Read train contents' is turned on, Include Train Fuel Info into Train Stops.

Effective distinguishing between wagon cargo signals and locomotive fuels signals would require Please, PLEASE make circuit connection behavior configurable per wire.

[Factoruser]

I'm just stuffin' in what's available. But it might be nice to have a ≤33% fuel level condition, so you don't have to send a train to the filling station although it's not necessary. I like to set up filtering circuits, although it's much too and unnecessarily complicated with the current combinators.