move YOLO examples into ObjectDetector

[lindapaiste]

Fixes #1145

I'm unsure of the status of existing PR #1183

For p5, move the existing YOLO examples into the ObjectDetector folder and rewrite ml5.YOLO(modelReady) as ml5.objectDetector("yolo", modelReady). I also cleaned up the YOLO single image example because I didn't like the order of execution (it assumes that the model loads before the image).

For JavaScript we already had YOLO examples in ObjectDetector so I just deleted the duplicates in the YOLO folder.