Add Export as Support

[pderckx]

In the Online Version of the tool there is an option to export the bpmn as svg or png. That would be very helpful if this add-on had it, too.

Suggestion: Save it per default at the same location with the same name as the .bpmn but with .svg extension.

[nikku]

We're currently re-writing this extension and will investigate this feature in the process.