Enforce no arguments for single-word commands

[ianyong]

Changes:

• Restrict the user from entering arguments for single-word commands.
  • clear
  • exit
  • help
  • list (including variants)
• Update tests accordingly.
• Minor spelling/grammar corrections.

Note that I did not end up using the parsers as it would result in a lot of repetitive code. In addition, using the parsers would mean that the error message that is shown cannot be customised to display the entered command, as there would be no way of disambiguating between the various list variants.

Fixes #280.

[codecov-io]

Codecov Report

Merging #281 into master will increase coverage by 0.05%.
The diff coverage is 83.33%.

@@             Coverage Diff              @@
##             master     #281      +/-   ##
============================================
+ Coverage     71.17%   71.22%   +0.05%     
- Complexity      920      921       +1     
============================================
  Files           141      141              
  Lines          2859     2871      +12     
  Branches        337      338       +1     
============================================
+ Hits           2035     2045      +10     
- Misses          703      704       +1     
- Partials        121      122       +1     

Impacted Files	Coverage Δ	Complexity Δ
...s1_cs2103_w16_3/finesse/commons/core/Messages.java	0.00% <ø> (ø)	0.00 <0.00> (ø)
...ookmarkparsers/AddBookmarkIncomeCommandParser.java	93.75% <ø> (ø)	5.00 <0.00> (ø)
...rkparsers/ConvertBookmarkExpenseCommandParser.java	100.00% <ø> (ø)	4.00 <0.00> (ø)
...arkparsers/ConvertBookmarkIncomeCommandParser.java	100.00% <ø> (ø)	4.00 <0.00> (ø)
...arkparsers/DeleteBookmarkExpenseCommandParser.java	100.00% <ø> (ø)	2.00 <0.00> (ø)
...markparsers/DeleteBookmarkIncomeCommandParser.java	100.00% <ø> (ø)	2.00 <0.00> (ø)
...6_3/finesse/logic/parser/FinanceTrackerParser.java	93.24% <83.33%> (-1.92%)	43.00 <1.00> (+1.00)	⬇️

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[yongping827]

LGTM

[wltan]

LGTM!