Allow overriding subject label language in CLI and REST suggest operations

[osma]

Fixes #628

This PR implements an option --language / -L for the annif suggest command as well as an optional language parameter for the REST API suggest method, both of which allow overriding the language of returned subject labels.

TODO:

• [x] error handling: don't break if the given language is broken or not available in the vocabulary
• [x] implement the --language option for the annif index command as well
• [x] address QA tool complaints

[codecov[bot]]

Codecov Report

Base: 99.61% // Head: 99.58% // Decreases project coverage by -0.03% :warning:

Coverage data is based on head (3cfcac8) compared to base (597e67e). Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #630 +/- ## ========================================== - Coverage 99.61% 99.58% -0.04% ========================================== Files 87 87 Lines 5945 5990 +45 ========================================== + Hits 5922 5965 +43 - Misses 23 25 +2 ``` | [Impacted Files](https://codecov.io/gh/NatLibFi/Annif/pull/630?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=NatLibFi) | Coverage Δ | | |---|---|---| | [annif/cli.py](https://codecov.io/gh/NatLibFi/Annif/pull/630/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=NatLibFi#diff-YW5uaWYvY2xpLnB5) | `99.68% <100.00%> (+<0.01%)` | :arrow_up: | | [annif/rest.py](https://codecov.io/gh/NatLibFi/Annif/pull/630/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=NatLibFi#diff-YW5uaWYvcmVzdC5weQ==) | `96.22% <100.00%> (-3.78%)` | :arrow_down: | | [tests/test\_cli.py](https://codecov.io/gh/NatLibFi/Annif/pull/630/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=NatLibFi#diff-dGVzdHMvdGVzdF9jbGkucHk=) | `100.00% <100.00%> (ø)` | | | [tests/test\_rest.py](https://codecov.io/gh/NatLibFi/Annif/pull/630/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=NatLibFi#diff-dGVzdHMvdGVzdF9yZXN0LnB5) | `100.00% <100.00%> (ø)` | | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=NatLibFi). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=NatLibFi)

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[sonarcloud[bot]]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
2 Code Smells

No Coverage information
0.0% Duplication