Extends creator to support modifying created objects

This should create a new component for editing object in Creator, clicking upon a particular object should open a Edit Page Area form which will enable users to edit it. I've created a new component called EditPageArea that has pretty much the same elements that were in the old AddPageArea, but it only accepts the object to be edited, as well as some of the properties from the page that contains that object. Regarding AddPageArea, I've modified it so that it contains only a snapshot from the area to be added and the type of the object to be created. I've not fully tested it yet, so it might need some more work :)

@leinir