QmlDesigner: Try to create the puppet only once

Change-Id: I0a56617b262a97e8b5d8007276ebaa09c8cbe4f6
Reviewed-by: Nikita Baryshnikov <nib952051@gmail.com>
Reviewed-by: Thomas Hartmann <Thomas.Hartmann@digia.com>
QmlDesigner.PropertyEditor: Remove unused files

The GenericPropertiesWidget is completely out of scope
and unused.

Change-Id: Ibd43bca724e87cca2d5f639e5bc9999a1f9af6ce
Reviewed-by: Marco Bubke <marco.bubke@digia.com>