Switching from WYSIWYG to Wiki edit mode while CKEditor is in Source mode messes up the edited content

Follow this steps to reproduce:

• Edit a page in WYSIWYG edit mode
• Switch CKEditor to Source mode
• Switch to Wiki edit mode (you need to be an advanced user)

The wiki syntax is messed up as a consequence. The reason is because the edit mode switch doesn't trigger any event so CKEditor doesn't get to update its internal fields before the page is submitted. The fix would be to:

• trigger a JavaScript event before switching edit modes
• catch this event in https://github.com/xwiki-contrib/application-ckeditor/blob/master/plugins/src/main/resources/xwiki-save/plugin.js#L74 along with beforePreview and beforeSave