Add Javadocs and refactor code to improve readability

[atyhamos]

No description provided.

[codecov]

Codecov Report

Merging #206 (2db2b3b) into master (6f23faf) will increase coverage by 0.07%.
The diff coverage is 84.21%.

@@             Coverage Diff              @@
##             master     #206      +/-   ##
============================================
+ Coverage     80.15%   80.23%   +0.07%     
- Complexity      718      719       +1     
============================================
  Files            96       96              
  Lines          2157     2160       +3     
  Branches        266      267       +1     
============================================
+ Hits           1729     1733       +4     
+ Misses          358      357       -1     
  Partials         70       70              

Impacted Files	Coverage Δ
...edu/address/logic/parser/PaymentCommandParser.java	84.21% <0.00%> (ø)
src/main/java/seedu/address/ui/TuteeCard.java	0.00% <ø> (ø)
src/main/java/seedu/address/ui/UiManager.java	0.00% <0.00%> (ø)
...in/java/seedu/address/logic/parser/ParserUtil.java	92.85% <83.33%> (+0.79%)	⬆️
...c/main/java/seedu/address/model/tutee/Payment.java	86.44% <100.00%> (+0.47%)	⬆️
...n/java/seedu/address/storage/JsonAdaptedTutee.java	100.00% <100.00%> (ø)
...du/address/logic/commands/DeleteLessonCommand.java	96.77% <0.00%> (+0.10%)	⬆️

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