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.
 
Can you calculate P outside the loop function? The involved variables are not modified inside the loop, meaning for every lens we are calculating the same value.