Add a config option to tweak the height of oil spouts.

[AlexIIL]

Specifically an option for the maximum height that an oil spout can generate. While we're at it, why not also add options for a lot of the other hardcoded numbers? If we add a lot then it would be a good idea to add another section to worldgen - possibly

worldgen { 
    oil_spout {
        small_min_height
        small_max_height
        large_min_height
        large_max_height
    }
}

[AlexIIL]

Implemented by @scagood in #4271, and will be a part of 7.99.19 at some point in the future.