WFS update, and added function for rectangular setups in the main

Increased the readability of mainWFS.py.
Normalized the intensity distribution and the lensletCentx/y.
Added support length for FFT in the parameters for the sensors.
Added function in main to handle rectangular lenslet configurations.
 
It is not needed. The number Nx represents the number of pixels on the axis x. Thus, the length of each pixel is simply:

lx/Nx

Same goes for the y.