Support for Error Correcting Tournament in vw_multi backend

[osma]

Part of #230

[codecov]

Codecov Report

Merging #252 into master will increase coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master    #252      +/-   ##
=========================================
+ Coverage   99.28%   99.3%   +0.01%     
=========================================
  Files          51      51              
  Lines        2386    2431      +45     
=========================================
+ Hits         2369    2414      +45     
  Misses         17      17

Impacted Files	Coverage Δ
annif/backend/vw_multi.py	100% <100%> (ø)	⬆️
tests/test_backend_vw.py	100% <100%> (ø)	⬆️

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[osma]

This pull request fixes 1 alert when merging 4877f30 into b3163f8 - view on LGTM.com

fixed alerts:

• 1 for Unused import

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Comment posted by LGTM.com