Calling functions directly on Object will result in non-virtual calls,
calling functions on AbstractObject will result in virtual calls. Also
removed now unneeded "hacks" like `sceneObject()` and properly hiding
unsafe functions taking `AbstractObject*` with safe functions taking
`Object*`. Also hide `isScene()` from public documentation, as it is
sort-of hack too.
The downside of this is that the functions are now virtual, which makes
them slower than before. Maybe final qualifier would help?
AbstractObject::sceneObject() is marked as private in Object to avoid
confusion.
Functionality present in Object is now split into three main components:
* Object itself, handling parent/children relationships
* Transformation implementation and interfaces for common functionality
* Object features, providing transformation caching and base for
cameras, collision shapes, rigid bodies etc.
Some functionality depending on former implementation is temporarily
disabled and will be reworked later.