Adds navigation keys to access past commands

[Michaeliaaa]

Allows user to use the up and down button to navigate past commands in the command box and help users to save time from re-typing the command again.

[gsmoon97]

LGTM! Maybe you could add some test cases for this functionality later?

[Michaeliaaa]

LGTM! Maybe you could add some test cases for this functionality later?

Yes, definitely. I will try to figure how to test peekNext() and peekPrev().

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@5741283). Click here to learn what that means.
The diff coverage is 72.00%.

@@            Coverage Diff            @@
##             master      #67   +/-   ##
=========================================
  Coverage          ?   69.96%           
  Complexity        ?      442           
=========================================
  Files             ?       77           
  Lines             ?     1405           
  Branches          ?      140           
=========================================
  Hits              ?      983           
  Misses            ?      382           
  Partials          ?       40           

Impacted Files	Coverage Δ	Complexity Δ
src/main/java/seedu/address/ui/CommandBox.java	0.00% <0.00%> (ø)	0.00 <0.00> (?)
...va/seedu/address/model/history/CommandHistory.java	96.66% <100.00%> (ø)	16.00 <9.00> (?)

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