Rename <import> to <model>

[tparisi]

is overloaded, esp. with Web Components ( tag has import rel type, used to do HTML import)

[tparisi]

Hmm or should this just use the <scene> tag with a 'src' attribute? They're really just imported scenes. One big implication of this is that a scene can have scenes as children. That's OK with me. Looking for input on this one.

[ailadson]

i'm leaning towards <model> because it makes the different use cases more explicit. the docs say that <scene> defines the root element. i think having different tags for the root scene and imported scenes is a good idea, even if it's all the same under the hood.