Make mutation loss weaken relevant categories

Previously, the only time that a category was weakened was a chance for a small (1/8th the increase of a single mutation) decrease when mutating a different category.

This resulted in category strengths constantly increasing across the board and meant that even if you completely removed all mutations, you were still highly weighted towards the category you were mutating towards.

Now, when you lose a mutation, the category is weakened. From the tests I've done it makes overall category strengths lower than they used to be, and you will more heavily trend towards categories you're mutating into. However, downing enough purifier will cause the categories to be reset to 0, allowing to start again if you want to.