Fix, can't set material parameters on default material instance

[bejado]

Setting material parameters on default material instances has no effect- i.e., the following:

MaterialInstance* instance = material->getDefaultInstance();
instance->setParameter("myParameter", RgbType::LINEAR, {1.0, 0.0, 0.0});

This happens with both float and sampler parameters. I'm a bit surprised this hasn't been discovered yet, so maybe I'm missing something.

Also, I think the UBO usage flag for the default material instance should match explicitly-created instances (DYNAMIC) unless we want the semantics that the default instance's parameters aren't meant to change...