Trigger rendering the preview on type

[Chris2011]

This could be done via option, maybe not everyone wants this and in the current state it will be a bit of flacky, but changes in the source should be immediately seen in the preview tab. Atm I need to hit save to trigger the rendering and after save I see it flecking, the progressbar is coming (v0.0.5) and this should not happen, if we have a rendering on type. Maybe not everyone wants this, so there should be an option for this "Render on save or render on type". Let the user decide.