Attach FieldObserver to the particle as well
Attach FieldObserver to the particle as well

-- Previously we attached the FieldObserver to the MagFieldArray to measure field changes, however now we need to also attach it to the particle, so that when the particle measures the next field at some position, it can send a notification to the field observer to update itself. 

-- Note though that the FieldObserver's subject is still ONLY the MagFieldArray.
mjrasobarnett/ucnsim,mjrasobarnett/ucnsim,mjrasobarnett/ucnsim