Visualize that a component is coming from a mixin

[vincentfretin]

See #689 (comment) for the context where we have mixins setting a gltf-model component.
Currently in the right panel we don't visualize that a component is coming from a mixin and that removing a mixin will remove associated components. Changing background color could be an enhancement here.

[vincentfretin]

If you know how Unity prefab works, you can see prefab instance as blue, and you can see the overrides you have on it
https://youtu.be/PSKKQKr2bnA?t=352
prefab is at the entity level, mixin is a bit similar, but more granular as a set of components.

What I had in mind was to have a different color for each mixin and the associated components that it is setting:

If you change the gltf-model here is this screenshot, it would lose the blueviolet background color and maybe say overridden label next to it. That may not be the great example here with such a simple mixin setting gtlf-model, you would just remove the mixin, but you get the idea.