Make filtered contact list reactive to contact additions/modifications

[kokrui]

Resolves #180 as per discussed implementation

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (abcfadc) 82.61% compared to head (d2d0502) 82.59%.
Report is 9 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #217      +/-   ##
============================================
- Coverage     82.61%   82.59%   -0.03%     
  Complexity      754      754              
============================================
  Files            99       99              
  Lines          2335     2332       -3     
  Branches        261      261              
============================================
- Hits           1929     1926       -3     
  Misses          337      337              
  Partials         69       69              

Files	Coverage Δ
...va/seedu/address/logic/commands/AddAltCommand.java	88.50% <ø> (-0.14%)	⬇️
...java/seedu/address/logic/commands/EditCommand.java	94.40% <ø> (-0.05%)	⬇️
...edu/address/logic/commands/UpdatePhotoCommand.java	85.29% <ø> (-0.43%)	⬇️

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[lordidiot]

LGTM! Thanks for working on this.

We can think about adding regression tests on all/most commands to ensure that we don't accidentally revert this in future.