QtGrahicsItem addToGroup don't work as expected

When ou add items in scene, rotate/scale then using setRotation/setScale and then if you group them the items have their transformation applied twice.

The code for grouping items is not clean. I suggest to either :

• make QtTransform aware of rotation and scale transformations not used via a matrix
• undo scale and rotation after applying the transformation matrix when placing items in a group (like it's done with position information)
• only use QtTransform matrix for transformations and get rid of double informations like position/rotation/scale
• deprecate grouping