[CR]Vehicle<->grid connector

[Coolthulhu]

A furniture part that connects a vehicle to a non-vehicle power grid.

Current limitations that need to be fixed:

• Includes a horrible hack regarding positioning. May require some redesigning to fix.
• No "load balancing" between grid batteries and vehicles
• Jumper-cable-connected vehicles not supported
• Vehicles don't "push" excess power to grid
• Vehicle "finding" code is slow and duplicates existing vehicle::find_vehicle (I wish I checked existing code first - it has exactly what I wanted)
• Jumper cable connection to the connector is hacky and disables regular "out of possession" cable handling
• Out-of-bubble processing

[Firestorm01X2]

@Coolthulhu are you going to enable power grid by default now or sometime later?

[Coolthulhu]

Probably with this PR, but it might take a while to get it to work.
I'm basically connecting "jumper cable grid" and building grid into one system here and it has multiple quirks.

[Coolthulhu]

Alright, this is pretty near completion.
Anyone willing to help with the code quality? I probably made a bunch of questionable decisions in there.

[Coolthulhu]

OK, I fixed all the problems I could find.
Grids are currently rather bare feature-wise, so there may be bugs that will only show later, when real features show up.

I tested it like this:

• Spawned a bunch of vehicles and connectors, connected them into a long line (long enough to exclude at least one from the bubble)
• Spawned laser-turret-equipped vehicle and used it to drain the battery
• Confirmed all vehicles have drained batteries
• Turned engine on one of the vehicles
• Waited for a long while
• Confirmed that batteries and vehicles outside of the bubble got charged

Plus there's some test backing, but less extensive than my manual test. It might be worth adding a long chain test, but this thing is already over 2 weeks old, so I'd rather just get it in and fix it later.

Comments requested, especially code quality hints.

[Coolthulhu]

Experimentally giving it a go