[AndyB] Featured images 2.8

Now supports WebP attachments.

Featured images are now square.

Added Log errors to options page.

Featured images v2.5 changes. Now compatible with XenForo Cloud. If upgrading from previous version, please create a new directory /data/files/featured_images using File manager, also the Options page Image URL field needs to be updated.

Improved error handling code.

Fixed issue with image selection condition.

Updated abstracted file system code.

Featured images v2.1 changes:

Updated andy_featured_images.less template.