Unify style and proprerty tools

[hilaire]

Until now the style and property tools are distinct:

- to edit the style the user goes to the palette icon, then select an item in the canvas, a side bar appears to let the user adjusts the item' style
- to edit the property of an item: point coordinates, free value, curvilinear abscissa, the user selects the wrench icon, then clic on the item to edit, then a dialog appears to edit the property.

The two could be put together, in the side bar for example. The benefit is to simplify the access to these two aspects of an item, easier for the user to discover both in one shot. Dynamic vertical panels could be used to do so.