added test cases for parser util, add expense parser

[nicleejy]

Some test cases for utility functions yet to be written.
Merge to incorporate sample expense and recurring expense data.

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: +2.43 🎉

Comparison is base (de46f89) 47.58% compared to head (cafcd72) 50.02%.

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #224      +/-   ##
============================================
+ Coverage     47.58%   50.02%   +2.43%     
- Complexity      493      526      +33     
============================================
  Files           109      109              
  Lines          2482     2483       +1     
  Branches        265      266       +1     
============================================
+ Hits           1181     1242      +61     
+ Misses         1195     1126      -69     
- Partials        106      115       +9     

Impacted Files	Coverage Δ
src/main/java/fasttrack/commons/core/Messages.java	0.00% <ø> (ø)
...rc/main/java/fasttrack/logic/parser/CliSyntax.java	88.88% <ø> (-3.97%)	⬇️
...c/main/java/fasttrack/logic/parser/ParserUtil.java	76.81% <100.00%> (+57.97%)	⬆️

... and 11 files with indirect coverage changes

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