Added two new symptoms to virology. They will mutate the victim and randomly set a power/disability block, after cleaning it to remove remaining powers/disabilities. One symptom only sets powers and the other only sets disabilities.

Changed the virus mix reaction to only require one plasma or mutagen, to remove the annoyance that virology has with the randomness aspect of it.

Refactor'd dna code to be a little tidier.
Fixed a typo which was preventing powers from manifesting properly.
Merge pull request #3021 from Giacom/viro_genetics

Added two new symptoms to virology.