ckeditor extend more for serendipity

This hides the ckeditor image widget button by CSS in all supported Serendipity toolbars, but keeps it internal functionality enabled which is needed for MediaLibrary inserts.
This forces the user to use the specialized ML button for image inserts only, but will still be supported by CKE toolbar.
An Image double click will still use the image widget like before.
Best checked place was to put this in admin/style.css.

References 148