Scripting: Fix an error with SceneNode.RotateX/Y/Z().
Fix an issue where OnStartup() wouldn't always get called.
Silenced an annoying warning.
Add the framework for the new message system for better handling error, warning and log messages.

Relates to issue #92.
Add some early work to the new EngineContext system.

This commit loosely affects issues #92, #74 and #45.
Some more work on the new audio system.

This loosely relates to issues #74.
Start using the new audio system.

This loosely relates to issue #74.