Add a picture to the given campaign's id

Adds image to a campaign. These types are valid:
'image/jpeg', 'image/gif', 'image/png'. Image aspect ratio should be 2:1. If not, autocrop of image's center will be done.
You can select the type of crop (cropType - 0 -> 512 x 256, 1 -> 512 x 512) and a specific platform ( platform - ios, android, webpush, safari) for which the image will be used. In the case of a gif image, which is composed of 3 frames, you can select the frame that will be used as a preview with the parameter defaultImg.