Fix the wrong transparent object menu buttons

[takahirox]

This PR fixes #4416 by introducing renderOrder attribute to hubs-text and rendering the texts of object menu buttons at last.

The screenshot with this PR. Please compare with the one in #4416.

My understanding of the mechanism how the problem was caused and how this PR fixes is

• The text is placed in font of the slice9 and object
• All of them are transparent and farther objects should be render first
• Three.js determines the render order by checking the distance of objects from the camera to generally the center of the objects
• If object group is rotated and/or it is far from the camera, Three.js can wrongly render the texts earlier than object and slice9 (This is the limitation of the current render order decision algorithm)
• If it happens overlapped area of slice9 and object are not rendered because of depth test. This is the reason why currently texts can be transparent to background
• An easy solution would be to force the render order of texts to render them at last by using Three.js Object3D.renderOrder

[takahirox]

Ah, wait. Making the slice9 opaque would be simpler solution (but it requires #4470). Let me try tomorrow.

[takahirox]

Closing in favor of #4470