Asteroid mineral turfs rates and rescaling

Okay so mining was a little too easy.

- This scales the mineral droprates on the turfs back, which I've done extensive checking on (using the admin scanner) to a point where it's not as barren as before, but not so crazy easy for miners.
- Monster spawn rate was reverted to before, so monster hunting is viable if you'd like to do that again for fun.
- Plasma remains economical and plentiful on the asteroid, but not nearly as plentiful as iron.
- Upped gibtonite rate on low chance (east asteroid) turfs a little, so iron mining won't be as tedious.

As I said, I've done lots of testing on this to make sure it's fair for a high volume (sybil) amount of miners, and one miner can't solo fill all the needs of science in 5 minutes.