Wrote a base class for all InstanceTests* classes, which provides a watchdog and functions for creating tracked instances. These instances become auto-disposed and any created objects get deleted. Also useful for tracking session and user ID's of testing instances.

- Fully implemented Avatars and Property tests
- Updated all other tests to use above
- Added sample URLs, Vec3, Rotation and VPObject getter
- Removed "AsX" extensions
- Added auto-pumping to EnterTestWorld