Issue #291: Restrict Layout file format to SVG (dismine/valentina)

New issue 291: Restrict Layout file format to SVG

Susan Spencer:

Restrict the file format of the Layout file to SVG.

This keeps all elements of the drawing in the smallest file footprint, and is a non-prietary open data format, usable by both prioprietary and FOSS design tools.

This will be important when creating a workflow to interact with sewists.

The Layout utility is not intended to create the printed file.

The Export utility creates the printed file.

This is to improve Valentina’s user experience and workflow.