[CR] Vehicle electrical system improvements

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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 alternators), no plutonium will be consumed
    -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

TODO/ideas:
    - add a small, continous epower draw to running gas/plasma engines (simulates an ignition coil)
        -> as a result, if alternator is destroyed, engines will slowly drain battery
        -> if battery hits 0, engine stalls
    - discharge battery slightly when starting gas engines (simulates starter motor)
        -> as a result, batteries will be required to restart dead vehicles found in the street
    - add a small engine better suited to a generator, say power 20 (10 HP)
        -> a power 20 engine will have lowest possible idle rate of 1 battery-equivelant charge/turn
        -> alternately, make engine variable size actually affect power output
    - add a large alternator better suited to a generator, say epower 4500 (4.5kW)
    - add a 'generator control' part - automatically starts/stops engines on battery threshold
    - add a generator cart 'vehicle', using above components, to be found in hardware stores
    - limit alternators to engine locations?
    - prevent alternators from being installed with footpedals
        -> footpedals are overpowered at 70 power (35 HP), possible exploit for easy epower
    - add a 'fuel cell' part - produces epower directly from hydrogen (basically a reactor that uses hydrogen)
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