Update HistoryItem methods signatures

[yakky]

To clarify input parameters, ent_id argument has been renamed to comment_id. Update your code if it uses kwargs for HistoryEntity.delete_comment / HistoryEntity.undelete_comment

[coveralls]

Coverage remained the same at 97.824% when pulling 641934a on bugfix/history-item-docs into 087e10b on master.

[codecov]

Codecov Report

Merging #94 (641934a) into master (087e10b) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master      #94   +/-   ##
=======================================
  Coverage   96.32%   96.32%           
=======================================
  Files           7        7           
  Lines         870      870           
  Branches       63       63           
=======================================
  Hits          838      838           
  Misses         19       19           
  Partials       13       13           

Flag	Coverage Δ
unittests	96.32% <100.00%> (ø)

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Impacted Files	Coverage Δ
taiga/models/models.py	96.43% <100.00%> (ø)

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