QmlDesigner: Pass const values by references

Change-Id: I468b2bebec64680289b24044b0b4e3d5d734f604
Reviewed-by: Tim Jenssen <tim.jenssen@digia.com>
Reviewed-by: Marco Bubke <marco.bubke@digia.com>
QmlDesigner: Fix order of initialization

m_resIconSize is passed to m_iconProvider's ctor, so it should
be initialized first.

Change-Id: I7a5dfb648cce029869b1e8a36eee761a5bd46faf
Reviewed-by: Marco Bubke <marco.bubke@digia.com>