Fix bug where calorie data reset to 0 after editing

[junhui-phoon]

Fixed bug where calorie data reset to 0 after editing.
A copy of the Calorie Manager is parsed to the Day constructor since every edit command creates a new Day object.
Since edit command does not edit any calorie values, this fix does not affect the integrity of Calorie Manager.

[codecov-io]

Codecov Report

Merging #124 into master will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##             master     #124      +/-   ##
============================================
+ Coverage     56.76%   56.78%   +0.02%     
  Complexity      467      467              
============================================
  Files            93       93              
  Lines          1811     1812       +1     
  Branches        191      191              
============================================
+ Hits           1028     1029       +1     
  Misses          700      700              
  Partials         83       83              

Impacted Files	Coverage Δ	Complexity Δ
...java/seedu/address/logic/commands/EditCommand.java	89.28% <100.00%> (+0.19%)	10.00 <0.00> (ø)

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[ethanso56]

looks good to me