- Improved Group::update_shape method, which now collects vertices from edges, not faces.
  Although this is a bit slower, it's more reliable since shapes can have no faces.
- Added ISG style, so we have uniform work environment.
- ISG_style.style renamed to ISG.style, as SketchUp didn't like it...
- Added Controller::prepare_model with corresponding files to set up SketchUp model.