QmlDesigner: Add allSubModelNodesAndThisNode to ModelNode

This is a pattern which is used very often

Change-Id: Ic2d05142149014c0f9d5b745df41522586a6f78b
Reviewed-by: Thomas Hartmann <Thomas.Hartmann@digia.com>
QmlDesigner: Add removeAuxiliaryData to ModelNode

it is the same like setAuxiliaryData with a invalid variant but more clear.

Change-Id: I23ab4050ebdcfe908ec9fdbc130c62ca24a717b7
Reviewed-by: Thomas Hartmann <Thomas.Hartmann@digia.com>
QmllDesigner: Refactoring to use allSubModelNodesAndThisNode

Change-Id: Ied8f2e9e10163f46c862edb6ee8e96a58a36bd71
Reviewed-by: Thomas Hartmann <Thomas.Hartmann@digia.com>