Update checkstyle.xml to check public classes for javadoc comments

[qwoprocks]

No description provided.

[tankangliang]

LGTM

[codecov-io]

Codecov Report

Merging #128 into master will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master     #128   +/-   ##
=========================================
  Coverage     71.28%   71.28%           
  Complexity      440      440           
=========================================
  Files            81       81           
  Lines          1379     1379           
  Branches        143      143           
=========================================
  Hits            983      983           
  Misses          345      345           
  Partials         51       51           

Impacted Files	Coverage Δ	Complexity Δ
src/main/java/seedu/address/model/note/Note.java	75.00% <ø> (ø)	2.00 <0.00> (ø)
.../main/java/seedu/address/model/tag/TagFactory.java	0.00% <ø> (ø)	0.00 <0.00> (ø)

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