Fully complete VR UI

There is a good baseline implementation in the project already that covers the SimulationControllerWidget, but choosing a new simulation at runtime is not yet possible.
Firstly we need keyboard input to work in VR to enter the simulation paths and secondly we need to show the SimulationLoading prompt instead of the SimulationControllerWidget when pressing a specific button.

Start by locating the existing SimulationControllerWidget implementation and the SimulationLoading prompt. Trace how the current VR UI handles button input and simulation paths, then determine where keyboard entry and runtime simulation selection belong. Done means paths can be entered in VR and the specified button shows SimulationLoading instead of SimulationControllerWidget.

Written by the indexing model from the issue text.