Make fast version of SymptomManager

[tbhallett]

In profiling, a lot of time is taken in SymptomManager. This is because it is designed to do a lot of checking (that the symptom exists, and the disease is allowed to apply it, and when its resolved its only resolved by the disease that caused it).

Whilst these checks are useful in development, now that we never have problems, we can dispense with these checks.

We should we create a drop-in replacement for SymptomManager that has the same functionality and interface, but internally does the simplest and quickest thing possible. This could be making all the symptoms columns bools