Add show method to visualize the laser

[RemiLehe]

This addresses #183. This adds a basic plotting capability (useful e.g. to make sure that the laser is fully inside the box, before dumping to disk).
For more advanced plotting, the user should probably dump the laser to file, and then use openPMD-viewer.

I also made use of this method in the tutorial:

[hightower8083]

do you think we could have here some kind of envelope=True option and in the case of False show the carrier-frequency resolved field from get_full_field?

[AngelFP]

Hi @RemiLehe, thanks for this.

Overall it looks good to me, and it makes me think again that we should make the Grid a smarter class (e.g., so that it knows its dimensions, extent, etc.). It is otherwise quite cumbersome to work with it.

[MaxThevenet]

@hightower8083 I would be in favor of only supporting the envelope in general, and avoid the carrier frequency, as it does not bring more information but is much more expensive. It's not a strong opinion, would be happy to hear everyone's thoughts.

[RemiLehe]

Yes, we can discuss this in the next meeting, and, if needed, do a follow-up PR. For now, since this is approved, I will merge.