Optimize default avatars to use less materials

[Aitolda]

As they are, the default avatars use a number of materials ("Sara" using 8 materials, etc), so if you have several avatars onscreen the number of materials in a scene can add up VERY quickly, leading to eventual bottlenecks.

While there is nothing we can currently do in regards to people bringing in their own avatars (or maybe just a popup suggesting no more than two materials), we can certainly adjust the default avatars offered.