Fixes

- GlobalState.Camera is now CameraComponent.Main.
- OnUpdate now takes float delta argument.
- SceneRenderer now longer requires update rate.
- Scene.Update takes float delta argument to support adaptive or fixed
width updates.
- Task InitialDelay and RepetitionDelay properties are now floats
instead of ints.
- GraphicsContextBase.OnUpdate delta property is a float instead of a
double.
- CameraComponent now has a parameterless constructor.
- Added Drag property to RigidbodyComponent.
- Hack: environment bounding box root extents are now 2 million cubed
instead of 2000 cubed.