Update plots.py

[HMEUW]

Added new function section_plot.

[OnnoEbbens]

Thanks for the PR! Before we merge could you add these two things?

1. An example of this function to an existing noteook ('01_groundwater_observations.ipynb')
2. A test function in the module test_008_visualisation.py

Let me know if you have any questions or you want so help doing this

[HMEUW]

I just made the last updates.

The last two suggestions are to be included later. For now:

• the near bottom of screen check can be chosen by keyword argument: check_obs_close_to_screen_bottom
• layout of legend outside plot. Nice layout (i.e. number of columns) depends on length of legend items