Add ObservableDirectory

[jeannetoh99]

No description provided.

[codecov-io]

Codecov Report

Merging #110 into master will decrease coverage by 0.07%.
The diff coverage is 52.83%.

@@             Coverage Diff              @@
##             master     #110      +/-   ##
============================================
- Coverage     56.69%   56.61%   -0.08%     
- Complexity      825      833       +8     
============================================
  Files           161      162       +1     
  Lines          3048     3091      +43     
  Branches        376      373       -3     
============================================
+ Hits           1728     1750      +22     
- Misses         1201     1224      +23     
+ Partials        119      117       -2     

Impacted Files	Coverage Δ	Complexity Δ
...rc/main/java/seedu/address/ui/TravelPlanPanel.java	0.00% <0.00%> (ø)	0.00 <0.00> (ø)
...eedu/address/model/travelplanner/ModelManager.java	42.34% <54.54%> (-0.39%)	18.00 <0.00> (ø)
...dress/model/travelplanner/ObservableDirectory.java	64.70% <64.70%> (ø)	8.00 <8.00> (?)

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[jiaweiteo]

LGTM