Delete image when repeater block is deleted

Previously, when deleting a repeater image block, the source file was not deleted. This addresses that issue and deletes the source file through the ImageProcessor. This makes is super easy to customise the delete functionality for remote drivers such as Cloudinary.

Important: If you created your own ImageProcessors and these do not extend the packages base image processor you will need to update them to ensure that they either extend Dewsign\NovaRepeaterBlocks\Processors\ImageProcessor or include a static delete method as shown in the Readme.