Fix edit doctor and patient bugs

[derekjxtan]

Fix nric change not cascaded to appointments.

Notes: Edit patient/doctor now behaves like a database transaction. If there is an error editing appointments, doctor/patient will not be updated as well.

[codecov[bot]]

Codecov Report

Merging #159 (69edfa9) into master (d8d1720) will increase coverage by 0.44%. Report is 34 commits behind head on master. The diff coverage is 97.05%.

@@             Coverage Diff              @@
##             master     #159      +/-   ##
============================================
+ Coverage     82.35%   82.80%   +0.44%     
- Complexity      740      762      +22     
============================================
  Files           105      108       +3     
  Lines          2148     2210      +62     
  Branches        214      218       +4     
============================================
+ Hits           1769     1830      +61     
- Misses          347      348       +1     
  Partials         32       32              

Files	Coverage Δ
src/main/java/seedu/address/model/Database.java	99.00% <100.00%> (+0.24%)	:arrow_up:
src/main/java/seedu/address/model/Model.java	100.00% <ø> (ø)
...rc/main/java/seedu/address/model/ModelManager.java	95.87% <ø> (ø)
.../main/java/seedu/address/model/UniqueItemList.java	98.38% <100.00%> (+0.27%)	:arrow_up:
...s/commons/util/lambdautil/CheckedFunctionUtil.java	80.00% <80.00%> (ø)

... and 3 files with indirect coverage changes

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