FIX: Removing max and min values after de-normalization of data-set, so the is_normalized() method will again return 'False' after de-normalization.

FIX: Removed 'normalized' and 'de-normalized' evaluation as there is just 'de-normalized' natively from now.

FIX: fixed an issue with NaN in GradientDescent caused by acos(x), added more debug info to errorfunction validation