Allow the image cropper to scale the uploaded file lower than 1.0

[markadrake]

If the image cropper allowed us to scale down further than 1.0, an editor could make this image fit the given dimensions.

Minimum and maximum scale values could be turned into a configuration value and defined on the data property, with sensible defaults left in place. If we use the current defaults, this would result in no change to pre-existing properties.