Implement Prescription UI

[joshenx]

Changes

• Abstracted addPrescription method to Model. @huyuxin0429 take note.
• Time and Date now shown separately on AppointmentCard
• Methods implemented in Appointment class to retrieve Time and Date in UI-specific format
• Known bug: adding a second prescription to the same Appointment is not reflected until the card is selected.

[codecov-commenter]

Codecov Report

Merging #152 (9d0df36) into master (50efb68) will decrease coverage by 0.16%.
The diff coverage is 17.64%.

@@             Coverage Diff              @@
##             master     #152      +/-   ##
============================================
- Coverage     53.39%   53.23%   -0.17%     
  Complexity      551      551              
============================================
  Files           116      116              
  Lines          2326     2337      +11     
  Branches        269      269              
============================================
+ Hits           1242     1244       +2     
- Misses          997     1006       +9     
  Partials         87       87              

Impacted Files	Coverage Δ
.../commands/prescription/AddPrescriptionCommand.java	9.09% <0.00%> (-0.44%)	⬇️
...c/main/java/seedu/docit/model/AppointmentBook.java	55.55% <ø> (ø)
src/main/java/seedu/docit/model/Model.java	100.00% <ø> (ø)
...a/seedu/docit/model/prescription/Prescription.java	0.00% <0.00%> (ø)
src/main/java/seedu/docit/ui/AppointmentCard.java	0.00% <0.00%> (ø)
...ava/seedu/docit/model/appointment/Appointment.java	40.90% <40.00%> (-0.12%)	⬇️
.../java/seedu/docit/logic/commands/ClearCommand.java	100.00% <100.00%> (ø)

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[huyuxin0429]

lgtm, very well done Joshen. I'll be giving you equal share + 200% for this commit alone. LGTM!!!!