Simplify GLTF map loading

[wendivoid]

Currently the process to load maps from gltf looks something like this:

load gltf asset -> 
    mark all entities created with a marker component ->
    iterate through these adding components as necessary

This process could be simplified if/when Rapier3d components implement Reflect, to skip step 3 & possible 2.
Currently I'm using a custom GLTF loader to parse the extras field and store the value alongside the entity, If we simple added the components added in step 3 when loading the initial GLTF asset