Change default file ending for SVG export to .dst.svg

[hschwentner]

Is your feature request related to a problem? Please describe. When you see a file foo.svg you’ll know it’s an SVG file but you can only guess if it was exported by Egon.io and thus contains DST file metadata.

Describe the solution you'd like [A clear and concise description of what you want to happen.] Make the default file ending for SVG exports .dst.svg instead of .svg similar to e.g. Draw.io. In the above example this would mean to have foo.dst.svg. It’s important not to use .svg.dst so other programs will still interpret the files as SVG.

Describe alternatives you've considered [A clear and concise description of any alternative solutions or features you've considered.]

Additional context Draw.io stores by default in .drawio.svg files.