Adds vending machines

Right now they only spawn at subway stations and in front of gas stations, but I'll add them to some more buildings in another commit. Any ideas for vending machine locations would be appreciated!

The default vending machine is sealed like a crate, and you can smash the glass with a bit of effort. This turns it into a "broken vending machine", which can be looted and further bashed into pieces. Both broken and unbroken variations will spawn, and broken ones are more likely to be pre-looted when the player finds them. They will spawn with either drinks or junk food inside.