Consolidate error messages

[dextertanyj]

Resolves #149

[codecov-io]

Codecov Report

Merging #206 into master will increase coverage by 0.03%.
The diff coverage is 94.54%.

@@             Coverage Diff              @@
##             master     #206      +/-   ##
============================================
+ Coverage     82.67%   82.70%   +0.03%     
  Complexity     1065     1065              
============================================
  Files           148      148              
  Lines          3168     3174       +6     
  Branches        381      381              
============================================
+ Hits           2619     2625       +6     
  Misses          455      455              
  Partials         94       94              

Impacted Files	Coverage Δ	Complexity Δ
src/main/java/tutorspet/commons/core/Messages.java	0.00% <ø> (ø)	0.00 <0.00> (ø)
...ain/java/tutorspet/logic/commands/ExitCommand.java	100.00% <ø> (ø)	2.00 <0.00> (ø)
...ain/java/tutorspet/logic/commands/RedoCommand.java	100.00% <ø> (ø)	3.00 <0.00> (ø)
...in/java/tutorspet/logic/commands/ResetCommand.java	100.00% <ø> (ø)	2.00 <0.00> (ø)
...ain/java/tutorspet/logic/commands/UndoCommand.java	100.00% <ø> (ø)	3.00 <0.00> (ø)
...ic/commands/moduleclass/AddModuleClassCommand.java	100.00% <ø> (ø)	8.00 <0.00> (ø)
.../commands/moduleclass/ClearModuleClassCommand.java	100.00% <ø> (ø)	2.00 <0.00> (ø)
...spet/logic/commands/student/AddStudentCommand.java	100.00% <ø> (ø)	8.00 <0.00> (ø)
...et/logic/commands/student/ClearStudentCommand.java	100.00% <ø> (ø)	2.00 <0.00> (ø)
...c/main/java/tutorspet/logic/parser/ParserUtil.java	93.58% <ø> (ø)	22.00 <0.00> (ø)
... and 33 more

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[ruixuantan]

LGTM

[samlsm]

LGTM 👍