Fixes to make it possible to run installed package

[osma]

This fixes #196 and #199 which have prevented running Annif as an installed package.

[codecov]

Codecov Report

Merging #200 into master will increase coverage by <.01%.
The diff coverage is 75%.

@@            Coverage Diff             @@
##           master     #200      +/-   ##
==========================================
+ Coverage   98.58%   98.58%   +<.01%     
==========================================
  Files          44       44              
  Lines        1911     1913       +2     
==========================================
+ Hits         1884     1886       +2     
  Misses         27       27

Impacted Files	Coverage Δ
annif/default_config.py	100% <ø> (ø)
tests/test_cli.py	100% <100%> (ø)	⬆️
tests/conftest.py	100% <100%> (ø)	⬆️
annif/__init__.py	88% <60%> (+1.04%)	⬆️

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