Rebalances Ra2Bunker[1.1] to be more vanilla.

Bunker
- Durability lowered from 1500 to 900
- Requires machining research & construction skill 9 to build
- Terrain affordance requirement changed from Light to Heavy
- When a bunker is destroyed some metal slag is left behind
- Increased range from 30 to 35 tiles
- Increased the cover from 40% to 75% (same as a wall)
- Buildable with stone and metal only (modded included)
Light Bunker
Adds a lighter bunker variant which can't take as much punishment, can only be built with wood (and steel,) doesn't shoot as far, but it's available earlier in the tech tree and isn't as expensive.
Vanilla bunker graphic
Change the texture for the bunker to something more vanilla looking.

Github: https://github.com/Neceros/Ra2BunkerBalance

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MIT License; Copyright © 2020 Billy Barnes
