VR Menu fixes

The VR Menu is a feature-limited version of the menu shown on the desktop.
It's controlled via code using UIManager.PositionVRmenu
It's controlled by the user using button one (menu button) on vr controllers ("A" button on oculus touch controllers, and probably the application menu button on vive wands), See VRManager.HandleMenuButton, and VRControllerEventHandler for handling controller events from VR system.

Todo
- [ ] Get the VR Menu to show up in a good default position (straight ahead from default user position) when the application starts.
- [ ] Prevent the menu from disappearing beneath the data columns and/or floor when user is looking down and they press the menu button to move it. Keep it above the floor or above the data if data is shown, have it face the user's headset.
- [ ] another subtask