Refactor the facade API to create/get runs

[danielhuppmann]

As just discussed, this PR changes the API to create/get runs from the (implicit)

Platform.Run(model, scenario, version="new")

to the more pythonic

Platform.runs.create(model, scenario)

and a corresponding get

Platform.runs.get(model, scenario)

Maybe I'm a bit old-fashioned, but I'd still like to keep the default vs. non-default selection implicit in the get() method on the facade-layer.

fyi @pmussak @glatterf42

[glatterf42]

Thanks, looks good to me. One note, though: at the moment, the only place where we test providing the version parameter to runs.get() is in test_benchmarks, so it might seem untested by simply looking at test_run. It is tested, so things are fine, but the test location is not very intuitive.

[danielhuppmann]

At the moment, the only place where we test providing the version parameter to runs.get() is in test_benchmarks, so it might seem untested by simply looking at test_run.

Thanks for that observation, I added a test for that in the test_run.py

[meksor]

LGTM