Add a PDF with a marker and integrate it into the example launch file

[felixvd]

This would be another step towards a "Calibration for dummies" package, which is in my opinion desirable.

The marker size could be the real size of the PDF printed in A4 at 100% scale, and the marker ID could be whatever the correct thing to enter there is. I would have made this a pull request if I had managed to look that up within 10 minutes.

[marcoesposito1988]

Hi @felixvd,

this is a very good idea!

I actually wanted to keep this package tracking system-agnostic, but I could wrap it and create an "easy_handeye_aruco" package with dedicated documentation and resources. I will start as soon as I have the time (I am not hanging out in the lab a lot in this phase).

Thanks for the input!