Add special tags for doctors and patients

[kohkaijie]

Previously, tags consisted of any alphanumeric strings. I have updated the addressbook to only accept priority levels for patient tags as well as specialisations for doctor tags. Patients can only have a single tag while doctors can have multiple specialisation tags.

Updated test cases to handle new tag format. Will add more test cases in the next commit to cover all new methods created and to double check for the presence of possible bugs.

[codecov]

Codecov Report

Merging #153 (332ab00) into master (2f1dc7e) will increase coverage by 0.31%.
The diff coverage is 70.00%.

❗ Current head 332ab00 differs from pull request most recent head 7150975. Consider uploading reports for the commit 7150975 to get more accurate results

@@             Coverage Diff              @@
##             master     #153      +/-   ##
============================================
+ Coverage     65.99%   66.30%   +0.31%     
- Complexity      637      661      +24     
============================================
  Files           111      113       +2     
  Lines          2523     2591      +68     
  Branches        254      272      +18     
============================================
+ Hits           1665     1718      +53     
- Misses          760      767       +7     
- Partials         98      106       +8     

Files	Coverage Δ
.../address/logic/parser/AddPatientCommandParser.java	96.29% <100.00%> (ø)
src/main/java/seedu/address/model/tag/Tag.java	85.18% <100.00%> (+13.75%)	⬆️
.../java/seedu/address/model/tag/ValidDoctorTags.java	100.00% <100.00%> (ø)
...java/seedu/address/model/tag/ValidPatientTags.java	100.00% <100.00%> (ø)
.../java/seedu/address/storage/JsonAdaptedDoctor.java	100.00% <100.00%> (ø)
...java/seedu/address/storage/JsonAdaptedPatient.java	93.75% <100.00%> (ø)
...ain/java/seedu/address/storage/JsonAdaptedTag.java	100.00% <100.00%> (ø)
...u/address/logic/parser/AddDoctorCommandParser.java	31.81% <0.00%> (ø)
...in/java/seedu/address/logic/parser/ParserUtil.java	94.38% <88.23%> (-3.93%)	⬇️
.../java/seedu/address/model/util/SampleDataUtil.java	31.70% <0.00%> (ø)
... and 1 more

... and 2 files with indirect coverage changes

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