Issue281 handle invalid lines in training data tsv file

[juhoinkinen]

1. Handle lines that are missing tab in training data .tsv by giving warning for such line and continuing:

$ annif train tfidf-en trainingdata_with_invalid_lines.tsv 
creating vectorizer
warning: Skipping invalid line (missing tab): ""
warning: Skipping invalid line (missing tab): "A line without tabs"
Backend tfidf: creating similarity index

2. Hide full traceback for missing file:

Edit: missing file case is handled by issue #318.

This closes #281.

[codecov]

Codecov Report

Merging #299 into master will increase coverage by 0.07%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #299      +/-   ##
==========================================
+ Coverage   99.38%   99.45%   +0.07%     
==========================================
  Files          55       56       +1     
  Lines        2920     2959      +39     
==========================================
+ Hits         2902     2943      +41     
+ Misses         18       16       -2

Impacted Files	Coverage Δ
annif/corpus/document.py	100% <100%> (ø)	⬆️
tests/test_corpus.py	100% <100%> (ø)	⬆️
tests/test_exception.py	100% <0%> (ø)
annif/exception.py	97.14% <0%> (+9.64%)	⬆️

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[lgtm-com]

This pull request introduces 1 alert when merging ec3cc2c into b660eed - view on LGTM.com

new alerts:

• 1 for Unused import

[lgtm-com]

This pull request fixes 1 alert when merging 8786802 into 2fb6108 - view on LGTM.com

fixed alerts:

• 1 for Unused import