Way too many improvements!

[niroyb]

• Reduce number of arguments to apply_effect() and make_lego_brick()
• Refactor palette code : Correctly build a palette and assert it is valid.
• Separate lego palette generation from palette application.
• Fix dithering argument by using the Image.FLOYDSTEINBERG constant.
• Remove one of the write to disk loops in legofy_loop by keeping the frames in memory.
• Fix possible undefined index variable used for printing the frame number.
• Remove if checks before resizing. They were always true.
• Allow windows users to legofy images without image magick.
• Only generate a file name automatically if one is not supplied. Do not modify the supplied one.
• Close image ressources when done. Might not be necessary but was getting errors printed from PIL.
• Add tests to increase coverage.

[JuanPotato]

I would appreciate if you gave me a list of what you fixed or just general examples, I will merge this once I get home and look at it more.

[niroyb]

Updated the top pull request comment.