[Bug] - 3D / 3Dfactorised parameter final_nonlin has no effect for cores with more than 1 layer

[vdobrev1]

@Mvystrcilova, @pollytur
For the Basic3dCore and Factorized3dCore in 3dcores.py the parameter final_nonlin has no effect if the core has more than 1 layer the reason for this is a if statement that is aways true in the loop that defines all layers after the first one.

In the for loop defined here the variable l takes values from 0 to number of layers - 2 and the condition a few lines after (line 183) compares l to self.layers. The result of this comparison is aways True by definition for l. The same holds for the for loop defined here and if condition here (line 430)

[pollytur]

Thanks @vdobrev1
Seems like you are right because in the 2d core its always range(1, self.num_layers) (here, here and here)

So we will try to fix it