Refactor handling of AnimatedObjects

[leezer3]

This PR refactors AnimatedObjects so that they are a subset of the overarching UnifiedObject

Required by #684 in order to get the HierarchyAnimatedObjects working correctly, as these require a totally different update method.

TODO:

• Need to slim down and combine the methods.
• Provide a virtual Update() method within the UnifiedObject
• Can we get rid of some more of the excess parameters in some of these methods?
• Possibly convert a bunch of the AnimatedObject booleans to a flags enum??

[leezer3]

Hmm...

Structural issues are a major problem here :/
Far too much depending on being able to access deep within the CarSection / Elements.

This might want a rethink / major rework of the entire CarSection approach...

[leezer3]

https://github.com/leezer3/OpenBVE/tree/CarSectionRefactor

Marginally tested rework of the CarSection, to be used as an alternative to this. Appears to work 'better' but I'm not at all convinced with the entire ObjectState concept :/
Quite a bit of reference chucking about too, which I'm not thrilled by....

I think this one should actually allow the HierarchyAnimatedObjects to be used in a CarSection, but may well break in new and interesting ways.....