Install plugin for ShortMaterial in headless mode (#105)

Not for review. This is just to get an artifact to run in production.
There's probably a better way to organize this

**NB:** We don't need to keep compatibility with the `type_path`. I'm
only doing this to stay compatible with files being written in
production currently. I assume this might change.

studio/src/lib.rs

@@ -21,6 +21,7 @@ mod hierarchy;
 mod input;
 mod inspector;
 mod interaction;
+pub mod material;
 pub mod math;
 mod mixamo;
 mod path;
@@ -33,6 +34,7 @@ mod ui;
 pub mod viewport;
 mod world_grid;
 
+use crate::material::MaterialPlugin;
 pub use crate::{
     anim::AnimPlugin,
     bvh::BvhPlugin,
@@ -86,6 +88,7 @@ impl PluginGroup for CommonPlugins {
             .add(InspectorPlugin)
             .add(InterpolationPlugin)
             .add(ScenePlugin)
+            .add(MaterialPlugin)
             .add(SkyboxPlugin)
             .add(StudioInputPlugin)
             .add(UiLayerPlugin)