Display day and night on the objects visibility graph (PDF)

[AmauryCarrade]

Is your feature request related to a problem? Please describe.
The objects visibility graph, on the PDF version, is great to get an overview of what will be visible on a given date, but it lakes the information on if the object will actually be visible (i.e., when is the night).

Describe the solution you'd like
I suggest to add the sunrise and sunset hours on the graph. One would have to compute these hours for the given date and given location. We could display these dates on the graph using some icon, or maybe a change in color, like so:

If such a solution is used, one must check if the color is visible enough on a black-and-white print, and is contrasted enough to remain accessible (even on paper, it's important!).

Describe alternatives you've considered
N/A

Additional context
N/A

---

Thanks for this project!

[Deuchnord]

Thanks for the suggestion, as we discussed yesterday, we might rethink about the way the Sun rise/set is displayed in the graph too.

Yet, this will need the implementation of Kosmorro/lib#46.