The edit image styles form's cancel link should be styled a a button

Problem/Motivation

On the Edit image styles effect form (admin/config/media/image-styles/manage/large/add/image_crop) the cancel link is styled as a link when it should be styled as a button

There are three types of buttons supported in core and in the Seven style guide. Standard, primary, and danger.
It's important that the correct button types are used consistently throughout Drupal

Remaining tasks

Add the a button class to that link