Add Module class with preliminary testing

[rocketninja7]

No description provided.

[ji-just-ji]

Lecturer -> List
Null/W grade option
Year to 0-6

[rocketninja7]

Lecturer -> List Null/W grade option Year to 0-6

Thanks for the feedback! Just updated the PR with a commit to fix those issues!

[codecov-commenter]

Codecov Report

Attention: 115 lines in your changes are missing coverage. Please review.

Comparison is base (0dd42c1) 75.26% compared to head (692fe98) 70.36%.
Report is 19 commits behind head on master.

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Additional details and impacted files

@@             Coverage Diff              @@
##             master      #79      +/-   ##
============================================
- Coverage     75.26%   70.36%   -4.90%     
- Complexity      419      428       +9     
============================================
  Files            71       79       +8     
  Lines          1338     1505     +167     
  Branches        126      137      +11     
============================================
+ Hits           1007     1059      +52     
- Misses          301      416     +115     
  Partials         30       30              

Files	Coverage Δ
...rc/main/java/seedu/address/model/module/Grade.java	74.41% <74.41%> (ø)
...in/java/seedu/address/model/module/ModuleCode.java	21.42% <21.42%> (ø)
...main/java/seedu/address/model/module/Semester.java	57.69% <57.69%> (ø)
...n/java/seedu/address/model/module/Description.java	0.00% <0.00%> (ø)
...main/java/seedu/address/model/module/Lecturer.java	0.00% <0.00%> (ø)
src/main/java/seedu/address/model/module/Name.java	0.00% <0.00%> (ø)
src/main/java/seedu/address/model/module/Year.java	0.00% <0.00%> (ø)
...c/main/java/seedu/address/model/module/Module.java	0.00% <0.00%> (ø)

... and 1 file with indirect coverage changes

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[rocketninja7]

#67