Investigate getting rid of Login Manager non-VR scene.

[jackjansen]

If we could get rid of the current Login Manager scene, replacing it by a Lobby that could be viewed in VR, that would solve a lot of problems:

• It would help Investigate native Oculus implementation #18,
• it could incorporate the self-calibration,
• it would get rid of a lot of ugly code that waits for VR initialisation at the start of each scene.

Possibly some of the functionality (like logging in, and selecting representation and microphone) could be moved to a separate application/scene, without VR, which would save the relevant parameters to a separate config file (or in the registry, or in a Unity persistent preference).

The lobby scene would only allow creation/joining of sessions, and selecting experience and transport mechanism. And self-calibration.

Assigning to @nachoreimat for comments, mainly.

[jackjansen]

It turns out that the first bullet isn't relevant, see #18.

[jackjansen]

And a few hours later I now think again that it is important. It might also fix the problem with things becoming invisible after a scene change, because it might allow us to just use auto-loading of XR plugins.

[jackjansen]

All part of #43.