QmlDesigner: Check if the Qt installation is updated

We should recompile the puppet if the Qt installation is updated because
we use private API.

Change-Id: I841f83faa6b3cac11fbb6a8b8d3508006a4f6b2d
Reviewed-by: Marco Bubke <marco.bubke@digia.com>
QmlDesigner: Reset fallback default

Change-Id: I188249bc9de3db6a3d650fb27af906374948262a
Reviewed-by: Marco Bubke <marco.bubke@digia.com>
QmlDesigner: Loading of the plugin in initialize

No anymore in the constructor.

Change-Id: I680e3d7e9c1ad103e78332fb1a54e15c7601fad9
Reviewed-by: Marco Bubke <marco.bubke@digia.com>