feat(content): gatling gun for forts and museums

[chaosvolt]

Purpose of change

An item @hirohito1 had requested and gave some help with, that I've been tinkering with to a limited degree since the idea came up.

Describe the solution

1. Adds a .45-70 gatling gun. Currently picked a model (jfc so many different models of gatling and so hard to find good info on any given one) that gives me an excuse to use drum mags instead of the more well-known feed tray.
2. Added Broadwell drums, uses the 240-round version.
3. Added vehicle part definition for mounted gatling gun.
4. Added vehicle definition for gatling gun, uses changes to the basic layout as implemented in feat(balance): NPCs can now help push vehicles, adjustments to wooden cart wheels #3811.
5. Added vehicle groups for bastion fort vehicle spawns and museum/mansion spawns. The former only spawns a gatling gun instead of a cannon 10% of the time, while the latter is 50/50.
6. Applied the mentioned vehicle groups to the bastion fort, mansions, and museum, replacing previous instances of spawning the cannon directly.
7. Added broadwell drums to museum_guns and fort_crate.
8. Added a dismounted gatling at a low rate to antique_guns and antique_guns_with_ammo.
9. Added .45-70 to antique_ammo, museum_guns, and fort_powderbarrel.

Describe alternatives you've considered

1. If speedloaders worked good (see issue: Allow topping off partially-loaded firearms using speedloaders #3398) we could give the gatling the Bruce feed instead, which basically means it'd have a fixed 40-round capacity and mainly use (wooden and thus potentially craftable) 20-round loading blocks to top them off partway through firing. In theory we could hack that in as an altrnative magazine type, or just make the gun be a clip_size gun and make the player reload the bullets by hand until the feature is supported.
2. Saying "fuck it" and adding the 400-round Broadwell drum too.
3. Adding .58 Rimfire so the Civil War era bastion fort can have a Civil War era version of the Gatling.
4. Going the opposite direction and making this one of the .30-06 versions, depending on which ammo might be more common for the player to find.
5. Adding a lower-capacity craftable version for if the player finds a gatling somewhere but no magazine?

Testing

1. Checked affected files for syntax and lint errors.
2. Load-tested in compiled build.

Additional context

Handy links:

1. http://www.victorianshipmodels.com/antitorpedoboatguns/Gatling/gatling1874.html
2. http://www.victorianshipmodels.com/antitorpedoboatguns/Gatling/magazines.html

Display guns for the VFW hall (mainlining the Tankmod: Revived variant prolly) and military base could come as a followup, but figured I'd save that for another PR since that'll probably come with adding a vehicle definition for either a display-only humvee or even a mockup of the old Willys MB, so that the display group can spawn other stuff besides old-school artillery.

Checklist

[scarf005]

2023-12-06_09-37-35.mp4

2023-12-06_09-38-46.mp4