Add module data

[blaukc]

Created a ModuleMap class which is just a wrapper for a map from module code -> Module object, which will be useful for checking if a module exists and linking students to modules.

Not sure about quite a few things in this PR, like the location of the json file and how to the DataLoadingException when we read the module_data file.

[codecov]

Codecov Report

Attention: Patch coverage is 73.07692% with 7 lines in your changes are missing coverage. Please review.

Project coverage is 75.10%. Comparing base (7c90816) to head (783638d).

Files	Patch %	Lines
...main/java/seedu/address/commons/util/JsonUtil.java	54.54%	4 Missing and 1 partial ⚠️
src/main/java/seedu/address/model/AddressBook.java	66.66%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master      #32      +/-   ##
============================================
+ Coverage     73.93%   75.10%   +1.17%     
- Complexity      419      430      +11     
============================================
  Files            75       76       +1     
  Lines          1362     1386      +24     
  Branches        126      128       +2     
============================================
+ Hits           1007     1041      +34     
+ Misses          325      314      -11     
- Partials         30       31       +1     

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[taufiq]

This is stellar code 🔥 what can you not do @blaukc !