Spoke components import support.

[Exairnous]

In reference to the importer: Add support for importing Hubs components from glTF files #63

Description
Some components in GLB files generated by Spoke aren't imported:

• box-collider (should map to Ammo Shape, I think)
• spawn-point (maps to Waypoint with canBeSpawnPoint enabled).
• mirror (not currently supported by the add-on)

Aside from that, the Spoke specific component definitionss (of which background is also one, but it is currently supported) should be in their own subfolder.

To Reproduce
Steps to reproduce the behavior:

• Open Spoke.
• Create a new project and add the unsupported elements/settings (or open a scene with them).
• Export it as a GLB (File -> Export as binary glTF (.glb)...).
• Import it into Blender.
• Observe that the components aren't recognized.

Expected behavior
The components should be imported.

Additional context
Related issue: #124