Allow upload SVGs to issues

In github-bugreports it is not possible to upload svgs, so you have to upload them as txt.

That’s important for svg-optimizers, svg-renderers, svg-editors

On you can use e.g.
svg-link: Svg_example1.svg
svg Svg_example1.svg
which should render in your browser as
png: 236px-Svg_example1.svg

<?xml version="1.0" encoding="UTF-8"?>
<svg xmlns="" version="1.1" width="120" height="120">
  <rect x="14" y="23" width="200" height="50" fill="lime"  stroke="black" />

PS: I get an error:

Sorry, new users can only put one embedded media item in a post.
Sorry, new users can only put 2 links in a post.

so I’m not able to make a proper bug-report