SVG Scaling bug fix

Hi,  I just fixed a nasty SVG scaling bug in Projectlayer which I think is worth pulling upstream in case others are using this dialog from pronterface.  

The pull request is showing quite a divergence between my experimental branch and master (now that your experimental is gone), but the bug fixes are in 2e6dd82 and 0c548e6 and only really affect projectlayer.py.

Cheers,
Gary