Add support for remote datasets

[lewisjared]

Pull request

Initial cut of a RemoteDataset class for handling API-based queries. Haven't written any docs yet, but looking for some feedback on naming/structure etc.

The added notebook contains examples of the use of the class so that might be a good place to start

Please confirm that this pull request has done the following:

• Tests added
• Documentation added (where applicable)
• Example added (either to an existing notebook or as a new notebook, where applicable)
• Description in CHANGELOG.rst added
• Refactor database backend #195 (I'll rebase after that has been merged)
• Better error handling

See https://github.com/openscm/scmdata/pull/198/files/b76adbb979527cc5932cbb563ff53e98439372c8..05401af873aa00871777255382b36cc33c5ef855 for a summary of the changes

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[codecov]

Codecov Report

Merging #198 (af605c8) into master (cc45eb2) will decrease coverage by 0.13%.
The diff coverage is 91.66%.

@@            Coverage Diff             @@
##           master     #198      +/-   ##
==========================================
- Coverage   95.79%   95.66%   -0.14%     
==========================================
  Files          23       24       +1     
  Lines        2069     2189     +120     
  Branches      388      409      +21     
==========================================
+ Hits         1982     2094     +112     
- Misses         69       77       +8     
  Partials       18       18              

Impacted Files	Coverage Δ
src/scmdata/database/_database.py	100.00% <ø> (ø)
src/scmdata/remote.py	91.15% <91.15%> (ø)
src/scmdata/__init__.py	100.00% <100.00%> (ø)
src/scmdata/errors.py	90.32% <100.00%> (+2.32%)	⬆️
src/scmdata/run.py	96.17% <0.00%> (+0.29%)	⬆️

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