Add confidence ellipsoid reading

[calum-chamberlain]

What does this PR do?

This PR adds reading confidence ellipsoids directly from NLLoc hyp files to ObsPy events. This also copes with the confidence ellipsoid not being included in the NLLoc hyp files.

On opening I haven't included a test for this yet, but will add one soon.

Why was it initiated? Any relevant Issues?

NLLoc hyp files (at least for NLLoc v7) provide this and it was otherwise silently skipped

PR Checklist

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[megies]

A couple of minor comments, tests need fixing (see comment), otherwise looking good to me. 🚀

[megies]

Rebased and final touches