Currently global bootstrap uses "accuracy" in several different ways:
* For all parameters passed to LevenbergMarquardt.
* For all epsilon parameters passed to EndCriteria.
* As the upper bound on the final value of the cost function.

This overloading makes it quite inflexible. Instead:
* Allow passing optimizer and EndCriteria to the constructor, which
  allows full control over all parameters.
* Instead of checking the final value of the cost function, check the
  result type from the optimizer.

Also, cleanup LevenbergMarquardt optimizer: remove commented out code,
fix parameters passed to MINPACK.