Import SVG

## Expected Behavior
When importing an SVG file, the software should automatically convert the image into an SVG string and create a new `Goo.CanvasPath` in order to keep that element editable and scalable.

## Current Behavior
SVGs are getting imported as regular raster images.

## Possible Solution
`Goo.CanvasPath` and `Goo.CanvasPathModel` allow loading SVG data as string, so we need a parser to convert an imported SVG into a string, and generate a path we can edit.

Most likely this will happen once we can handle groups, as most SVGs come with multiple shapes inside, so for each shape a Path should be created, and the entire SVG should be converted into a folder group.

Do we need to use any particular library like `librsvg`, `gsvg`, or similar?