Make notes window reactive

[kokrui]

Closes #212

[codecov]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (33db2cf) 82.72% compared to head (499bd40) 82.73%.

Additional details and impacted files

@@            Coverage Diff            @@
##             master     #227   +/-   ##
=========================================
  Coverage     82.72%   82.73%           
- Complexity      763      767    +4     
=========================================
  Files           100      100           
  Lines          2356     2363    +7     
  Branches        262      263    +1     
=========================================
+ Hits           1949     1955    +6     
  Misses          337      337           
- Partials         70       71    +1     

Files	Coverage Δ
...c/main/java/seedu/address/model/person/Person.java	100.00% <100.00%> (ø)
src/main/java/seedu/address/ui/NotesWindow.java	93.02% <80.00%> (-1.72%)	⬇️

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[lordidiot]

LGTM! Thanks for working on this, works as expected 👍