Add ROS-agnostic 2D localization demo

[hidmic]

Feature description

Beluga boasts about being decoupled from ROS, but every single example and demo we have so far relies on ROS in one way or another. We need a demo, a basic 2D localization demo is enough, that proves it is possible to stay away from ROS.

Implementation considerations

Perhaps the trickiest part of this demo is going to be emulating or simulating the target system. An in-code simulation with MuJoCo may be the easiest to integrate in C++ while keeping code complexity low. There's also Drake, but that's a steeper learning curve.