Changes to featured image (post thumbnails) logged

Yep. Finally!

Here’s how it looks:

Also in this version:

• The preview image of uploaded images now uses the default WordPress image size small, instead of a custom image size. Also these mage previews are now abit smaller because many uploaded images could make the log a bit to long and not so quick to overview.
• JavaScript library Select2 is updated to the latest version.
• If a user is running a very old version of WordPress, that is incompatible with Simple History, a message is shown, informing the user that their WordPress is to old.
• An error with PHP 7.1 was fixed.