Simplify DomUI classes

Generate text/setText methods only for "mixed" elements,
other elements don't use this API.
Remove unused DomScript, DomImages, DomImage, DomImageData,
DomProperties, DomPropertyData, DomSizePolicyData, DomWidgetData.
Use default constructors and in-class initialization.
Format newlines.

Change-Id: Ic91c797de68710cabc36db1e99bdf82332107ebc
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>