Feature/maximum width or height transformer

New ImageTransformer that resizes the layer. Accepts two Integer params: height and width. Only width **or** height will be scaled and the other dimension will be calculated to keep original ratio. If the original image is smaller than the configured dimensions the image won't be resized
Typically we'd declare as:

`static final String PROP_ALLOW_UPSCALING_PROPERTY = "allow-upscaling";`

The fact that its maxwidthorheight is implied since thats the containing transformer.