Remove unused imports and declare dependencies used

[kinow]

Today I worked on a different project and decided to use click for the first time from scratch. Knowing Annif used it, I came right here to look for the setup.py to see what was there.

Only found click-log (interesting!), but not click. Then decided to look what other transitive dependencies were being used in the project.

I think the second commit covers all the dependencies used in code and tests. Added them to the respective groups of dependencies.

Cheers
Bruno

[kinow]

Oh, and to avoid the unused imports issue in the __init__.py, I exported the imported code via __all__.

[codecov]

Codecov Report

Merging #271 into master will decrease coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #271      +/-   ##
==========================================
- Coverage   99.31%   99.31%   -0.01%     
==========================================
  Files          52       52              
  Lines        2629     2623       -6     
==========================================
- Hits         2611     2605       -6     
  Misses         18       18

Impacted Files	Coverage Δ
tests/test_rest.py	100% <ø> (ø)	⬆️
tests/test_cli.py	100% <ø> (ø)	⬆️
tests/test_backend.py	100% <ø> (ø)	⬆️
annif/backend/__init__.py	100% <ø> (ø)	⬆️
tests/test_project.py	100% <ø> (ø)	⬆️
annif/corpus/__init__.py	100% <100%> (ø)	⬆️

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[osma]

Thanks @kinow, looks good!