Adding min_pixel and max_pixel to set_hough_properties

[cylammarco]

In set_hough_properties, min_wavelength and max_wavelength are referring to the wavelength at pixel 0 and the wavelength at the last pixel.

In some arcs, there are only lines in half of the frame, it would make sense to fit only the region where there are peaks. In any case, it would be generally easier to understand what the limits are when we twin-up the min_wavelength with a min_pixel, and a max_wavelength with a max_pixel.