Add UWB example

[ratheron]

Since UWB Meets Crazyflow is published now, I would like to add the code to replicate the results. I think this also adds useful examples on how to use Crazyflow. For this, I will create three PRs.

1. This one adds a simple UWB model and uses the noisy UWB position estimates directly in the controller
2. Adds an IMU model with drifting states. Since it doesn't make sense to fly with this, we just compare the real state to the IMU measurements.
3. Combines/reuses 1 & 2 and fuses the observations into an EKF. This is the experiment from the paper.

After those examples are in, I will tackle #131

[amacati]

How long is the final example? I am wondering if this should really be in here, or if we should put it in a separate repository and link to it in the docs as "examples of Crazyflow in other works". We could also link to the main experiments there. The main sim repo is not really a place for experiments from papers.

[ratheron]

Following our discussion, we will only include widely used sensors into the examples (such as IMU). I will generate the IMU PR later. I will look into simplifying the EKF example after.

In this PR, I will instead just link to projects that use crazyflow.