Add support for scale transforms in SVG import.

Original report:

When importing an SVG created with Inkscape, one of the elements (rectangle) is shifted (mirrored?) to the left.
The example (back.svg) is appended. If you open it with Inkscape, you see the rectangle should be above the "USB" label.

My impression is that the sign of the X coordinate is swapped for some reason. At least if I mirror it
using two points on the Y axis, it seems to appear where it should be.

Apart from this, also the dimensions are wrong after import. In the original SVG, the outer shape is 144.3mm wide.
This is also visible in the header of the SVG:

 width="144.300mm"
 height="53.800mm"

However, after importing to QCad, the width is measured as 40.7247. This is a puzzling factor of 3.5433 which doesn't look
like metric/imperial conversion issue but like a complete misinterpretation of the sizes/units used in the SVG.