Implement Delete Assignment command

[murtubak]

fixes #387

[codecov-io]

Codecov Report

Merging #388 into master will decrease coverage by 0.71%.
The diff coverage is 6.55%.

@@             Coverage Diff              @@
##             master     #388      +/-   ##
============================================
- Coverage     25.31%   24.59%   -0.72%     
- Complexity      339      341       +2     
============================================
  Files           176      181       +5     
  Lines          2864     2976     +112     
  Branches        332      349      +17     
============================================
+ Hits            725      732       +7     
- Misses         2074     2179     +105     
  Partials         65       65              

Impacted Files	Coverage Δ	Complexity Δ
...rc/main/java/seedu/address/logic/LogicManager.java	0.00% <0.00%> (ø)	0.00 <0.00> (ø)
...c/main/java/seedu/address/logic/ParserManager.java	0.00% <0.00%> (ø)	0.00 <0.00> (ø)
.../gradetrackercommands/DeleteAssignmentCommand.java	0.00% <0.00%> (ø)	0.00 <0.00> (ø)
...seedu/address/logic/parser/GradeTrackerParser.java	0.00% <0.00%> (ø)	0.00 <0.00> (?)
...a/seedu/address/logic/parser/ModuleListParser.java	56.00% <ø> (+4.14%)	10.00 <0.00> (ø)
...er/gradetrackerparsers/DeleteAssignmentParser.java	0.00% <0.00%> (ø)	0.00 <0.00> (ø)
...c/main/java/seedu/address/model/module/Module.java	20.65% <0.00%> (-0.23%)	6.00 <0.00> (ø)
...a/seedu/address/model/module/grade/Assignment.java	0.00% <0.00%> (ø)	0.00 <0.00> (ø)
.../grade/exceptions/AssignmentNotFoundException.java	0.00% <0.00%> (ø)	0.00 <0.00> (?)
...grade/exceptions/DuplicateAssignmentException.java	0.00% <0.00%> (ø)	0.00 <0.00> (?)
... and 10 more

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[jonasngs]

Overall the code structure is good and javadocs are neat and concise. However, there is a potential bug in the DeleteAssignmentParser class that should be rectified.