Refactor article Title as a class

[H4mes]

Closes #71

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 27 lines in your changes are missing coverage. Please review.

Project coverage is 48.85%. Comparing base (ee34dd3) to head (5788cec).

Files	Patch %	Lines
...c/main/java/seedu/address/model/article/Title.java	0.00%	15 Missing ⚠️
...in/java/seedu/address/logic/parser/ParserUtil.java	0.00%	3 Missing ⚠️
...java/seedu/address/storage/JsonAdaptedArticle.java	0.00%	3 Missing ⚠️
...c/commands/articlecommands/EditArticleCommand.java	0.00%	1 Missing ⚠️
.../address/logic/parser/AddArticleCommandParser.java	0.00%	1 Missing ⚠️
...main/java/seedu/address/model/article/Article.java	0.00%	1 Missing ⚠️
.../model/article/TitleContainsKeywordsPredicate.java	0.00%	1 Missing ⚠️
...eedu/address/model/util/SampleArticleDataUtil.java	0.00%	1 Missing ⚠️
src/main/java/seedu/address/ui/ArticleCard.java	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master      #87      +/-   ##
============================================
- Coverage     49.25%   48.85%   -0.40%     
  Complexity      452      452              
============================================
  Files           112      113       +1     
  Lines          2217     2235      +18     
  Branches        236      238       +2     
============================================
  Hits           1092     1092              
- Misses         1086     1104      +18     
  Partials         39       39              

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[Howlong11]

LGTM