* Make it possible to switch a placeholder shape into the shape it represents.

There are still some open points maybe someone has an idea: I would like to change the placehoder shape when you double click on it in the default tool.

That already works but it is not nice as the tool used for doing the change pops up in the tool box.
Also I'm not sure which shape is clicked when the placeholder tools is activated.
At the moment I use the first selected placeholder shape.