added cylindrical helix and straight(ish) beta strand cartoon rendering; modified ambient occlusion and local lighting model; some low-level gfx refactoring and tweaking tidbits; added vertex array capped cylinder; fixed scene centering

git-svn-id: https://dng.biozentrum.unibas.ch/svn/openstructure/trunk@2007 5a81b35b-ba03-0410-adc8-b2c5c5119f08