[Test] Add EpisodeXmlWriter tests

[bugwelle]

This PR adds further tests and fixes the NFO file generation of episodes.

[codecov-io]

Codecov Report

Merging #775 into master will increase coverage by 0.93%.
The diff coverage is 53.21%.

@@            Coverage Diff            @@
##           master    #775      +/-   ##
=========================================
+ Coverage    3.75%   4.69%   +0.93%     
=========================================
  Files         402     405       +3     
  Lines       33358   33451      +93     
=========================================
+ Hits         1254    1570     +316     
+ Misses      32104   31881     -223

Impacted Files	Coverage Δ
src/media_centers/KodiXml.h	0% <ø> (ø)	⬆️
src/tv_shows/TvShowEpisode.h	50% <ø> (+50%)	⬆️
test/helpers/debug_output.h	50% <0%> (-50%)	⬇️
src/ui/tv_show/TvShowWidgetEpisode.cpp	0% <0%> (ø)	⬆️
src/ui/export/ExportDialog.cpp	0% <0%> (ø)	⬆️
src/data/Database.cpp	0% <0%> (ø)	⬆️
src/media_centers/KodiXml.cpp	7.39% <0%> (+0.6%)	⬆️
src/scrapers/tv_show/TheTvDb.cpp	0% <0%> (ø)	⬆️
src/media_centers/kodi/EpisodeXmlWriter.cpp	100% <100%> (ø)
test/unit/tv_shows/testTvShowFileSearcher.cpp	100% <100%> (ø)
... and 15 more

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