Add optimization skipped note #31

When the optimized image resulted in a bigger file size, the optimization is skipped, and the original file is uploaded instead. When this happens it might not be apparent to the user that this happened, let's add a notice in the media manager (where the Cimo stats are displayed).

Display this message:

WebP conversion skipped
The WebP version of this image was larger than the original, so the original file was kept instead.
You can try lowering the image quality setting to generate a smaller WebP file.

Change the file type if needed.