Allow sorting of animals in lowercase

[m0nggh]

Resolves #299.

[codecov]

Codecov Report

Merging #300 into master will increase coverage by 0.04%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##             master     #300      +/-   ##
============================================
+ Coverage     74.87%   74.92%   +0.04%     
  Complexity      546      546              
============================================
  Files            83       83              
  Lines          1584     1587       +3     
  Branches        160      160              
============================================
+ Hits           1186     1189       +3     
  Misses          340      340              
  Partials         58       58              

Impacted Files	Coverage Δ	Complexity Δ
...java/seedu/zookeep/logic/commands/SortCommand.java	100.00% <100.00%> (ø)	6.00 <0.00> (ø)
...a/seedu/zookeep/model/animal/AnimalComparator.java	97.05% <100.00%> (+0.18%)	10.00 <0.00> (ø)

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