QmlDesigner: Split between bounding rectangle and painted bounding rectangle

In qml the interactive bounding rectangle is always
QRectF(0, 0, width, height). The painted bounding rectangle can differ from
this logical one. This change is much more near to the qml description.

Change-Id: I139cb70512fa1ed003b28ca2ae512f4e33e915e5
Reviewed-on: http://codereview.qt.nokia.com/812


Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Thomas Hartmann <Thomas.Hartmann@nokia.com>