Support for velocity and covariance

[andre-nguyen]

Hi @MichaelGrupp, thanks for the great work, love evo and use it fairly often.

Is your feature request related to a problem? Please describe.
One of the issues I often face is that I want to look at more than just poses, namely estimated velocity and uncertainty bounds.

Describe the solution you'd like

1. First would be plotting support for these data if they exist.
2. A new text file format or an extension to the TUM format which includes velocities and uncertainties.

Describe alternatives you've considered
🤷🏼‍♂️

Additional context
I can imagine that plotting multiple uncertainty bounds can get messy very quickly. Already, if your reference trajectory has uncertainty bounds, plotting two trajectories would create 6 curves and be hard to read. Maybe we would need an easy way to select which uncertainties are plotted?