empty test observation coverage plot

[Hendrik1987]

@ecomodeller and @jsmariegaard , working on the long list of ideas #132 will likely fix this, but I need an ad-hoc solution now :-)

I can think of two approaches:

1. Add fmskill.plot.plot_observation_coverage(), which can be called by the Connector or stand alone. This would be consistent with the other plot methods here, such as fmskill.plot.plot_observation_positions, which is called here.
2. Allow a connection without a model result: Connector([o1, o2, o3], '')

I feel that 2 is more overlapping with a general rework, so my proposal for now would be option 1.

Thoughts? Other options?

[ecomodeller]

The only way to get through a long list of tasks is to get started with the most pressing one...

[ecomodeller]

Should be pretty straightforward to extract
a separate method from this https://github.com/DHI/fmskill/blob/3c0bae70210924e52d356b5b8259c2e243b8aa8c/fmskill/connection.py#L589 to only the temporal coverage to plot a list of observation.

Create a function that make sense to you!

[Hendrik1987]

Thanks @ecomodeller .
Will give it a shot with mikeio.plot.plot_observation_periods() as sister to mikeio.plot.plot_observation_postitions().

[jsmariegaard]

This is being addressed in #187 - I suggest closing this PR.

[jsmariegaard]

Closed by #187