Change dietary requirements implementation

[keaganpzh]

Currently, the implementation of dietary requirements is a single value string that can either be present, none, or null.

This does not allow tracking of a guest with multiple dietary requirements.

To allow for tracking of multiple dietary requirements, let's:

• Remove the existing DietaryRequirements class and fields.
• Change the representation of dietary requirements in Guest to be a set of individual DietaryRequirement objects, i.e. Set<DietaryRequirement>.
• Update the UI to reflect this new representation.
• Rewrite all associated classes and test cases accordingly.

Addresses #132.

[codecov]

Codecov Report

Attention: 11 lines in your changes are missing coverage. Please review.

Comparison is base (ae77806) 79.98% compared to head (6d8711d) 80.07%.

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #141      +/-   ##
============================================
+ Coverage     79.98%   80.07%   +0.08%     
- Complexity      708      718      +10     
============================================
  Files           104      106       +2     
  Lines          2183     2233      +50     
  Branches        249      251       +2     
============================================
+ Hits           1746     1788      +42     
- Misses          388      396       +8     
  Partials         49       49              

Files	Coverage Δ
...c/main/java/wedlog/address/logic/LogicManager.java	73.07% <100.00%> (+1.07%)	⬆️
...og/address/logic/parser/GuestAddCommandParser.java	100.00% <100.00%> (ø)
...n/java/wedlog/address/logic/parser/ParserUtil.java	98.46% <100.00%> (+0.18%)	⬆️
...rc/main/java/wedlog/address/model/AddressBook.java	90.62% <100.00%> (+0.14%)	⬆️
...og/address/model/DietaryRequirementStatistics.java	100.00% <100.00%> (ø)
src/main/java/wedlog/address/model/Model.java	100.00% <ø> (ø)
...c/main/java/wedlog/address/model/ModelManager.java	100.00% <100.00%> (ø)
...c/main/java/wedlog/address/model/person/Guest.java	96.66% <100.00%> (ø)
...a/wedlog/address/model/person/UniqueGuestList.java	92.00% <100.00%> (+1.37%)	⬆️
...a/wedlog/address/model/tag/DietaryRequirement.java	100.00% <100.00%> (ø)
... and 5 more

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[tllshan]

Nice work! LGTM