HVR: Fix in game menu usage

[JaXt0r]

Currently (afaik?) the in game menu isn't usable with HVR's VR player. For XRIT we added custom logic to it. Let's do the same in here.

TODOs

• Check on XRIT's VRPlayer (Assets/Gothic-UnZENity-XRIT/Resources/Prefabs/VRPlayer/VRPlayer.prefab) on how the menu was added to it
• Try to reimplement for HVR Player
• Bind a button on Controller to open the menu
• (Bonus) Check if you can come up with a modular logic, which just sub-prefabs the same Menu logic, so that we don't need to build the menues twice (for each player - XRIT + HVR)