Don't strip participant declarations

Ref #3: ok I see that "show-region-not-full-file" is actually a feature and not a bug. Rendering the full file would end up in a very small not viewable image (unless u manual zoom in). So just rendering the current view is actually nice.

But my graphs have a `participant` declaration on top of the file which got lost and changed the layout of the graph depending on order and current view. Annoying!

This PR fixes this. Additional to the current view, it finds all `participant` declarations and add those on top.

**warning** this are my fist lines of Python and sublime plugin, so pls do it better ;)

thanks for the plugin!