Renamed the Apache function wrappers.

Created a generic NonLinearFunctioWrapper so that the function can be
used without knowledge of the fixed parameters.
Add check for saturated pixels
Updated comments on BOBYQA fitter
Use analytical gradient for Binomial
Updated comments of the derivative
Improved the fitting to use the BFGS optimiser with a bounded
sum-of-squares gradient function.
Changed the relativeOrAbsolute method to improve speed.