added class UserInterfaceAudioManager
added project Arena
added (and gitignored) models files to data.cfg
fixed cleanup of GraphicsTaskManager by just clearing upload thread group and waiting for worker thread
replaced usage of glPushAttrib() with class PushedAttributes
set default for option optionSkyMeshLines to false
apply render options every frame
set transparency of loaded jpeg images
use ObjectId instead of Uuid
fixed rendering sky and milky way skybox
added sky textures
fixed reading scanlines that span IDAT chunks