Use group id's to improve loading existing svg's

[peteruithoven]

SVG editor now stores group names into title elements, while software like Illustrator and Inkscape store it into attributes of groups.
Illustrator stores the layer name into a "id" attribute and Inkscape stores it into a "inkscape:label" attribute.

Using the id's to store the group name and copying it into inkscape:label would enable using these names across SVG editor, Inkscape and Illustrator.