Update class.pictureGenerate.php

Now autodetects the original image size (for noscript), I'm yet to see if Scott Jehl's pictureFill outputs width and height normally or if I'll have to modify his code to do it. Builds the markup based on the files being there - had to put in a way to validate whether the url was absolute or relative to distinguish whether from a CDN or local. Still have a lot of work to do to make this awesome, but it works pretty well for now.