Additional improvements to the bulk mesh upload: support more Collada! 

Specifically, this now supports something that the LL viewer doesn't: the ability for instances of geometries to reuse geometries specifications.

Imagine a track with many poles, each pole being the same geometry; the LL viewer requires a geometry element for every single pole! This patch makes libomv able to parse Collada files where instances reuse geometries, allowing for much more concise Collada files.