Adds Gibtonite, the explosive ore!

Gibtonite design doc:

-Gibtonite is a mineral found in deposits on the asteroid.
-Gibtonite is disguised as diamond deposits until the player attempts to mine them, at which point they activate
-After activating, a timer counts down, and the Gibtonite reserve will eventually explode if left alone.
-If you use an analyzer on Gibtonite, you can halt the countdown at any point, even immediately after activating it. However, the closer you were to it exploding before you defuse it, the better quality gibtonite ore you'll receive once you extract it. Effectively, if you do not like the thought of exploding, simply use your analyzer whenever you see a diamond deposit and you will never come to any harm, but risk takers get rewarded.
-Gibtonite mineral deposits (Ores behave differently), despite the name, will not gib you. You will instead take 96 damage, unless you're occupying the same space as gibtonite, so it's not an instant round removal in the event of failure.
-Gibtonite reserves CAN detonate eachother, but in my testing I have never seen more than 2 go off in sequence.
-Gibtonite ore cannot be pulled. You cannot pick up gibtonite without two free hands, due to its weight and awkard size. Gibtonite does not fit in a backpack. There is a very noticeable sprite. If you see a miner walking around the station with Gibtonite, I suggest alerting security and abandoning the area.
-Gibtonite ore can only be activated by striking it with a pickaxe/drill. You can still disable it with an analyzer to stop it from exploding, but keep in mind that this degrades the ore to its lowest quality.
-At this time, Gibtonite has no use R&D or Crafting, subject to change whenever.

Other changes:
-Changed ex_act() on asteroid mineral turf to not delete ores
-Reduced ex_act() on asteroid turf's chance to kick up sand, because it's more unnecessary clutter and nobody cares about sand.