VRTK, UI: Convert UI ID System to VR

### Current system
* Raycast center of screen
* Return GameObject hit by ray
* Look up its name in ItemDescriptions.cs
* Display (any) info on 2D UI
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### Proposed System
* Hold object
* ~~Look object up in ItemDescriptions.cs~~
* 3D world UI text displays info near bottom of object
* Have functionality for item info too
