Add animation support

[StjerneIdioten]

Add support for exporting animation keyframes

[StjerneIdioten]

• Characters: Animationsets in the i3d file
• Buildings: Some form of animationset in xml file
• Vehicles: "scripting" in the xml using this

The first two could be generated from keyframing in blender, the last could also be done like that. But people usually just script it directly in the file.

I3D Animation example download
Building xml example