Add option to change radius of gaussin filter

Add option to change standard deviation (std), which is related
to the radius of blurring of the gaussian filter.

By default -g=0 and the gaussian filter is not applied. Otherwise,
if an integer different than 0 is used, this integer indicates
the std/radius of the filter. Bigger it is, higher it is the
blurring effect of the filter.
Add option -f for using or not the average FF

In order to normalize, sometimes it is useful to use the averageFF;
but others some obtrusive diffraction patterns are present, and it
is preferred to use only one single FF image for the normalization.
In this case the first FF image is used [0 FF image].

To activate the normalization using the average FF: -f=1 (default)
To deactivate the normalization using the average FF: -f=0