Fix 818

[aulemahal]

Pull Request Checklist:

• This PR addresses an already opened issue (for bug fixes / features)
  • This PR fixes [sdba] bug with LOCI map_blocks for add_dims in Grouper #818
• Tests for the changes have been added (for bug fixes / features)
• Documentation has been added / updated (for bug fixes / features)
• HISTORY.rst has been updated (with summary of main changes)
• bumpversion (major / minor / patch) has been called on this branch
• Tags have been pushed (git push --tags)
• The relevant author information has been added to .zenodo.json

What kind of change does this PR introduce?

• Fixes to LOCI:
  • thresh is now a Quantity string, as it should be after Update history, refactor sdba processing functions, add unit handling in sdba #801.
  • The _loci_train function is now wrapped correctly to reduce dimensions passed in Grouper.add_dims, as it should have been in [sdba] Optimizations and fixes #791.
  • sdba.utils._ecdf_1d reduces along all dimensions, to allow the use of Grouper.add_dims with LOCI.

Does this PR introduce a breaking change?

No

Other information:

An announcement about Grouper.add_dims was added to the history.