Improve testing, update DG and fix UG bugs

[kerbysoh]

• Created tests for UniqueRoleList

• Improved tests for CompanyListParserTest, FindCommandParserTest and UniqueCompanyListTest

• Added Use Cases for favourite, listFavourite and unfavourite commands

• Fixed UG bugs with regards to dates

[codecov-commenter]

Codecov Report

Merging #282 (dfe52fe) into master (8a87ca0) will increase coverage by 1.45%. The diff coverage is n/a.

@@             Coverage Diff              @@
##             master     #282      +/-   ##
============================================
+ Coverage     66.68%   68.13%   +1.45%     
- Complexity      676      694      +18     
============================================
  Files           107      107              
  Lines          2203     2200       -3     
  Branches        259      258       -1     
============================================
+ Hits           1469     1499      +30     
+ Misses          629      607      -22     
+ Partials        105       94      -11     

Impacted Files	Coverage Δ
...a/seedu/tinner/logic/parser/FindCommandParser.java	95.45% <ø> (+35.45%)	:arrow_up:
...ain/java/seedu/tinner/logic/parser/ParserUtil.java	91.54% <0.00%> (+1.40%)	:arrow_up:
...n/java/seedu/tinner/model/role/UniqueRoleList.java	92.68% <0.00%> (+31.70%)	:arrow_up:
...a/seedu/tinner/logic/parser/CompanyListParser.java	100.00% <0.00%> (+33.33%)	:arrow_up:
.../model/role/exceptions/DuplicateRoleException.java	100.00% <0.00%> (+100.00%)	:arrow_up:

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