Allow LevenbergMarquardt Optimizer to use Generics (Lists) 

In todays programming the number of measurements is not allways known upfront. Therefore people will use Lists. To avoid cast and copy tasks it would be cool to provide a gerneric optimizer supporting lists. Also I would like to reuse the same optimizer whenever new data arrives with minimum of cost (i.e. restarting threads etc.). And I it is useful to know the error for the best fit, so I added a getter method for it. 

Maybe you would like to merge this class. 

Cheers
KIC

PS Maintaining should be an easy one sice the task is only to replace targetValues[index] by targetValus.get(index).doubleValue() - which could be done by find and replace.