Improvment for GAF-image generation

[nklsla]

Output images are now exactly as big as the calculated data + RGB-channels (i.e. 40x40x3 for code example). In comparison from before: There are no white border around the image which. It can now handle generic square-sized data (e.g. 2x2, 3x3, 4x4 etc.) The script runs significantly faster.