Vehicle electrical system improvements

    Gameplay changes:
        -gasoline/plasma engines no longer have built-in alternators
        -added 3 new alternator part types: motorcycle, car, truck
        -alternators will slightly reduce engine power available for vehicle speed/acceleration
                - > the bigger alternator (or multiple alternators) or the smaller the engine, the larger the effect.
        -alternator electrical load affects fuel consumption at idle.
                -> a vehicle with many lights, fridges, chargers, etc. will burn more fuel while idling.
                -> idle control allows for practical generator applications: power your workbench with gas instead of solar.
        -added alternators to appropriate pre-defined vehicles

        -reactors now produce electricity directly, instead of acting as fuel for electric motors
        -reactors only generate electricity on demand, so when your vehicle's electrical requirements are being met by other means (solar or
        -reactors can be turned on/off.
                -> install on your solar vehicles for use only at night or in an emergency
        -reactors now have a (very high) power output limit
                -> it is now possible to overload a reactor resulting in an electrical shortage.

    Under-the-hood changes:
        -added concept of electrical power 'epower' to vehicles, which is defined in watts
                -> the pre-existing 'power' property can be thought of as mechanical power.
        -all electrical parts now have an epower property
        -vehicle parts can have a positive or negative epower or power
        -alternators convert power to epower (ie. they have a negative power rating and positive epower rating)
        -alternators have a conversion efficiency of 50% to 60%
                -> So installing alternators on electric motors will only result in a net loss of power (just like real life!)
        -electric motors convert epower to power (i.e. they have a positive power rating and a negative epower rating)
        -electric motors have a conversion efficiency of 90% to 95%
        -all electric power accounting (production and consumption) is done in epower, with the final result applied to the batteries.
                -> This allows for small loads (e.g. the vehicle tracker) to have an impact on battery (and therefore fuel) over time.
        -epower sources are used in this order: solar, batteries, alternators(gas/plasma), then reactors(plutonium).
                -> common fuel is used first, exotic used last.
                -> reactors can be turned off and saved for emergencies.
        -engine idle speed controlled by alternator load, which varies based on vehicle epower load.
                -> Higher idle speeds will cause the engine to consume fuel at a higher rate.
        -fuel consumption is now also more granular.
                -> Lower fuel consumption at idle is now possible.

    Other changes/fixes:
        -added caches for alternators, engines, solar_panels, and reactors
                -> should make the game run faster in or around vehicles
        -made better use of existing fuel tank cache.
        -refresh caches on vehicle load.
        -added small storage battery to bubble car (acts as a buffer between the reactor and electic motor)
        -added missing car battery to cube van
        -added missing car battery to hippy van
bigger starting screen
-alternators can now only be installed on gas engines
-gas engines consume small amounts of electricity while running (for ignition system, ECU, etc.
-gas engines will die if battery hits 0
	-> exception: small engines (1 cyl) don't require electricity to run (they use a magneto instead)
-plasma engines produce electricity while running (output comparable to truck alternator)
-changed minimum idle rate to 1% of full throttle
add back the tutorial room from mapgen.cpp
Some construction and terrain tweaks

Can fill spiked pits(t_pit_spiked) to shallow pit
Boarding up empty window will create "t_window_boarded_noglass" instead of "t_window_boarded"
Walkway(t_bridge) gets "flat" flag
Breaking boarded window will create some glass shards
Empty window won't have "barricadable_window" flag anymore
You can board up empty window frame also (to "t_window_boarded_noglass")

New terrain : "t_window_boarded_noglass"
-will not create glass shards on breaking
-will become empty window instead of window frame
- discharge battery slightly when starting gas engines (simulates starter motor)
Merge pull request #5166 from talktips/construction

Fillable spiked pits and boarded up windows tweaks
Merge pull request #5158 from belenos-/vehicle_electrical_system

[Done] Vehicle electrical system improvements
Merge pull request #5173 from BevapDin/fix-tutorial

Add the tutorial room from mapgen.cpp to new mapgen_functions.cpp
Merge pull request #5165 from illi-kun/bigger_start_screen

Bigger starting screen