Add zoom handle for Group (PasteCanvas) layer
Add zoom handle for Scale layer
A better way to specify exponential property of zoom handles
Align Zoom handle to the focus point
Display the correct hint text when hovering on Zoom handles
Pass studio::Duck instead of synfig::Point to Duck::signal_edited. That allows to pass exponential flag to callback function via Duck object.
Merge Duckmatic::on_duck_angle_changed into Duckmatic::on_duck_changed

Also remove signal_edited_angle from Duck class
Merge pull request #42 from morevnaproject/zoom_handle

Add Zoom handle for Group layer and Scale layer