Maximize should use position:fixed instead of changing entire page styling

[Piotrek Koszuliński]

Follow up of ​http://dev.ckeditor.com/ticket/8587#comment:8

Using position:fixed for the editor chrome may be beneficial for us because it will need less code, there won't be a problem with input names, it may be faster and more stable. Additionally, we may check if there are other ways to remove scrolls from the viewport which will not cause so much damage underneath the editor.