Unroll Fisher diagonal calculation in the gradient calculators
Allow filtering using minimum photons as well as SNR
Moved calculation of the Maximum likelihood precision to the PeakResult.
Use this when filtering by precision if using a Maximum Likelihood
fitter.
Store the precision threshold as a square (i.e. variance threshold)
Allow computation of the precision/variance of a peak result (allowing
the sqrt to be avoided)
Added speed test for the calculation of the Maximum Likelihood
precision. Use 10 iteration points by default.
Use the default number of iteration points for ML variance
Changed default to not use SNR filtering but a min signal of 30 photons
and a precision of 40.
Add min photons to the filtering options.
Check min photons is positove