Rotating the projection box breaks scaling (Project Fill Layer)

*ArmorPaint 0.9-0afaed9, Windows*

**Issue description:**
When the projection box is rotated to one side, e.g. to project onto another surface, the scaling handles are changed as well - it destroys the previous scaling

**Steps to reproduce:**
Activate the projection box, scale it in Z to project a smaller / more precise area - rotate it

Start by reproducing the issue in the Project Fill Layer projection box using the listed ArmorPaint version and the Z-scaling-then-rotation steps. Inspect the projection box rotation and scaling entry points; done means rotating the box preserves the previously chosen scaling and still projects the intended smaller area.

Written by the indexing model from the issue text.