[ENH] Keywords - language from corpus

[PrimozGodec]

Description of changes

• Make YAKE and RAKE modules to use ISO language
• Use language from the corpus for the Keyword Extraction widget
• Fix sorting in LanguageModel and add tests

Includes

• [X] Code changes
• [X] Tests
• [ ] Documentation

[codecov-commenter]

Codecov Report

Merging #961 (153e06f) into master (7456311) will increase coverage by 0.07%. The diff coverage is 97.05%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #961      +/-   ##
==========================================
+ Coverage   82.27%   82.34%   +0.07%     
==========================================
  Files          93       93              
  Lines       12448    12474      +26     
  Branches     1699     1705       +6     
==========================================
+ Hits        10241    10272      +31     
+ Misses       1895     1892       -3     
+ Partials      312      310       -2