[MERGED PR] Purgatives and dialysis machine rebalance

[aft2001]

Honestly more interactions between medicines and other chems, both positive and negative, would probably enhance the doctoring experience a good deal. Apex medicines like pent and perf having negative effects when combined with other medicines is, I think, a good idea. New players also aren't much more likely to get confused or overwhelmed, since these interactions should be for the 'advanced' medicines.

The dialysis machine is indeed neat, and I'd like it to be more commonly considered when I'm diagnosing/treating people, and the above would definitely help.