Added scene::factory and scene::factoryOgl to indirect creation of GL types, etc.  Cleaned up use of auto to use ref types in almost all new range-for statements.  Duh.  Implemented convenience scene/framebuffer setup methods in renderSink, but will probably move those to a different place (maybe derived class in application code).  Changed fbo discard logic a little to dump everything, but still seeing some logical buffer ops in GL traces.  Might be due to some slightly off buffer setups.  Introduced depth component image and texture types.  Introduced scene::uniobj to cache uniform lookups.