refactored backbone trace and simplified trace renderer base (e.g. removed...

refactored backbone trace and simplified trace renderer base (e.g. removed trace subset class or overshooting concept)
careful examination of all spline related code, array access via .at instead of [] and other failsafe mechanisms placed to either avoid core dumps or locate them better, tweaked generated spline range to have proper spline-list size
added temporary interface for cartoon detail color range
fixed/improved refresh/rebuild behavior for entity and its renderer objects, especially for offscreen rendering purposes
re-added fast spheres for CPK rendering
removed a few unnecessary asserts and exceptions
removed some old undefed code



git-svn-id: https://dng.biozentrum.unibas.ch/svn/openstructure/trunk@2121 5a81b35b-ba03-0410-adc8-b2c5c5119f08