All distributions to uniform, fixes #961

[amirDahari1]

Changed the norm_to_uniform function to all_to_uniform function, to fix #961 since not all distributions that are needed for a specific porosity are normal, including the blobs distribution.

[amirDahari1]

Added porosity argument to fractal_noise generator to fix #963. I'm not sure if to keep the uniform argument or not, since porosity already needs the transition to uniform, but thought to keep it for the case when the user prefers the uniform distribution without thresholding.

[jgostick]

I am going to merge this PR, then sort out the broken examples afterwards. Thank you very much for this!.