Svg headless export

[gfontorbe]

Following @jbicker draft PR (#439)

• I added options to select the download folder and filename
• Close the browser when the download is done
• Updated sprotty action to change the export file name if specified

Next:

• Have the save directory path resolved from a relative path

[jbicker]

I will take over this one again in regard of this.

[spoenemann]

This is now solved with #454.