Update certain fields to become optional

[PrestonTYR]

resolves #45
resolves #48
resolves #49
resolves #34

I think i might be missing some test cases

[codecov-io]

Codecov Report

Merging #58 into master will decrease coverage by 3.50%.
The diff coverage is 52.22%.

@@             Coverage Diff              @@
##             master      #58      +/-   ##
============================================
- Coverage     76.09%   72.59%   -3.51%     
- Complexity      492      498       +6     
============================================
  Files            77       78       +1     
  Lines          1523     1613      +90     
  Branches        171      188      +17     
============================================
+ Hits           1159     1171      +12     
- Misses          321      381      +60     
- Partials         43       61      +18     

Impacted Files	Coverage Δ	Complexity Δ
.../java/seedu/address/model/util/SampleDataUtil.java	10.00% <0.00%> (-10.00%)	1.00 <0.00> (ø)
src/main/java/seedu/address/ui/PatientCard.java	0.00% <0.00%> (ø)	0.00 <0.00> (ø)
...java/seedu/address/storage/JsonAdaptedPatient.java	75.75% <42.85%> (-24.25%)	17.00 <0.00> (-6.00)
...main/java/seedu/address/model/patient/Patient.java	86.53% <58.62%> (-11.09%)	36.00 <6.00> (+6.00)	⬇️
...java/seedu/address/logic/commands/EditCommand.java	97.95% <100.00%> (+0.02%)	12.00 <0.00> (ø)
...a/seedu/address/logic/parser/AddCommandParser.java	100.00% <100.00%> (ø)	5.00 <0.00> (ø)
.../seedu/address/logic/parser/EditCommandParser.java	94.59% <100.00%> (ø)	16.00 <0.00> (ø)
...in/java/seedu/address/logic/parser/ParserUtil.java	98.48% <100.00%> (+0.12%)	29.00 <15.00> (+5.00)
...a/seedu/address/model/medicalnote/MedicalNote.java	42.30% <0.00%> (ø)	6.00% <0.00%> (?%)

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