I've coded again

With this patch, one can convert all enginetypes to all other. You select the engine to convert and the one to convert to, independent which one has which track-type. If a to-be-converted engine enters a depot, it will be replaced (as normal), but it will stay in the depot, if it can't leave it (Monorail can't drive out of electric depot for example). If all your trains are converted and waiting in depot, you convert all your tracks (as normal) and start all trains again. See screenshots.
I don't think this qualifies as a patch, it looks more like a hack to me. Perhaps some ottd-code-experts can suggest improvements...
TODOs:
* Find better solution for power-calculation (outside of VehicleEnter_Track())
* Replacement for red flag in depot-window for trains that can't leave the depot
* Replacement for start-stop-button-string in vehicle-window for trains that aren't allowed to be started
So long,
Haukinger