Change the methods implemented by GraphicsMagickToolkit and required by GraphicsMagickToolkitInterface
The following methods implemented by `GraphicsMagickToolkit` and required by `GraphicsMagickToolkitInterface` should be removed.
* `extensionFromImageFormat()`
* `mimeTypeFromImageFormat()`
* `imageFormatFromExtension()`
`getFileExtension()` should be added as new `GraphicsMagickToolkitInterface` method.
issue