Use graphicsmagick as node module instead of command

[aloncarmel]

Use gm as node module dependency and not command line local install, This will let users use imagemagick instead for convert.

• Side question, whats the idea behind the .png convert? why isnt ffmpeg being used to convert from movie to gif all together?

[aloncarmel]

ffmpeg -i yesbuddy.mov -pix_fmt rgb24 output.gif for example

[jnorris441]

I assume it's because the ffmpeg palette for GIF is fixed, so the resulting GIF looks terrible. I wish there was a way around that since skipping the PNGs is so much faster...