Fix GUI related Bugs

[yanghengtang]

The following issue is resolved in this PR

1. Help Window not giving the right link (Closes #217)
2. Sample data wrong NRIC for patients and doctor (Closes #232)
3. View Windows not showing after minimised (Closes #218, Closes #214)

[codecov[bot]]

Codecov Report

Merging #236 (9876e91) into master (8fd3fc2) will decrease coverage by 0.23%. The diff coverage is 0.00%.

@@             Coverage Diff              @@
##             master     #236      +/-   ##
============================================
- Coverage     81.04%   80.81%   -0.23%     
  Complexity      938      938              
============================================
  Files           137      137              
  Lines          2823     2831       +8     
  Branches        275      275              
============================================
  Hits           2288     2288              
- Misses          502      510       +8     
  Partials         33       33              

Files	Coverage Δ
.../java/seedu/address/model/util/SampleDataUtil.java	0.00% <ø> (ø)
src/main/java/seedu/address/ui/HelpWindow.java	0.00% <0.00%> (ø)
.../main/java/seedu/address/ui/AppointmentWindow.java	0.00% <0.00%> (ø)
src/main/java/seedu/address/ui/DoctorWindow.java	0.00% <0.00%> (ø)
src/main/java/seedu/address/ui/PatientWindow.java	0.00% <0.00%> (ø)

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