Example of Bevy's standard material defined externally

For use with bevy 0.11

See for reference: https://github.com/bevyengine/bevy/blob/main/crates/bevy_pbr/src/pbr_material.rs https://github.com/bevyengine/bevy/blob/main/crates/bevy_pbr/src/render/pbr.wgsl

This also swaps out any instances of the standard material with the custom included material. (see swap_standard_material())