Add support for putting dedicated "Insert Macro" buttons on the tool bar

The old GWT-based WYSIWYG editor has the ability to add dedicated "Insert XXX Macro" buttons on the tool bar. See http://platform.xwiki.org/xwiki/bin/view/AdminGuide/WysiwygEditor#HAddan27InsertHTMLmacro27buttononthetoolbar . We need to support this with the CKEditor integration also.