Implementing lazy operators in express

[Erik-Chagas]

This is an implementation of lazy operators in express using the lazy parameter in QuantumOpticsRepr.

This will close #117.

[Krastanov]

Apologies for having missed this -- please do not hesitate to send a ping if you do not receive a PR review in a reasonable time span. It is easy to miss a PR, especially if it is not in my review queue.

Thanks for the contribution! This seems to be on the right track, but as you can see, most test are failing. I think you need to also modify the representation type to include this new lazy field you are assuming to exist in the rest of your code. I will mark this as a draft for now. Feel free to mark it back as ready if you feel like finishing it.