Small fixes for website combability

[runemadsen]

Hi @REAS and @benfry

This PR fixes a few small things for website compability:

1. Since example .pde files need to be named based on their parent folder, I renamed Topics/File IO/SaveOneFrame/SaveOneImage.pde to Topics/File IO/SaveOneImage/SaveOneImage.pde
2. Since the old website used just the name of the example (and not the categories) in the URL and we wanted to keep the old routes working, examples with the same name will overwrite each other. The only examples that do this are the two Brightness examples, so I renamed Basics/Color/Brightness to Basics/Color/BrightnessPixels

If any of these changes pose problems to the PDE, I can also add specific handling in the website script to do it, but I figured it would be better to standardize things. I want to rewrite the URL generation of the new website to support examples with the same name, but that will probably not be right now.

[REAS]

Great, I think this is "all good." Thank you.