Update IBTrACS to version 4.1

[ChrisFairless]

Changes proposed in this PR:

This year IBTrACS updated from version 4.0 to 4.1 and on May 28th the last v4.0 dataset was posted to their site.

That means anyone using CLIMADA is using IBTrACS data that hasn't been updated since then, even if they're regularly redownloading the file.

This PR points everything to the location of the new download and updates the tests because some of the tested values have changed.

Changes in v4.1:

• There's a new provider, KMA, the South Korean agency, with associated columns. I haven't updated CLIMADA for that: this would require someone to find out their wind averaging period and add it to tc_tracks.py
• It looks like a lot of values have been changed but I haven't looked into what and how much. Many appear to be due to a change in rounding somewhere in the data creation (lat, lon, pressure, wind). Since IBTrACS only gather and summarise data from other bodies, there shouldn't be big changes. Either way, NOAA consider this an improvement on previous versions of the data and we don't have a choice about using it. I had to update some of the tests because of this
• The TRACK_TYPE column now includes 'PROVISIONAL' as a possible value, which labels provisional US data (A-Deck). These are updated to 'Best Tracks' (B-Deck) by HURDAT after each season ends. It's information only, pointing out something that IBTrACS did already. Nothing in CLIMADA Core uses this column

The (rewritten) tests for the unit all pass.

Note:

• Users who have previously downloaded the v4.0 data will be left with it on their machine and might not be aware. It's ~25 MB so not tiny but not huge.

PR Author Checklist

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• [x] Descriptive pull request title added
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• [x] Documentation updated
• [x] Tests updated
• [x] Tests passing
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• [x] Changelog updated

PR Reviewer Checklist

• [x] Read the Contribution Guide
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[peanutfun]

Thanks a lot for this PR, @ChrisFairless! 🙌 I am currently on parental leave and will not be able to review until January. Maybe somebody else would be willing? @spjuhel @NicolasColombi

[spjuhel]

Happy to give this a look next week!

[NicolasColombi]

Happy to have a look as well!