Implement feature: Assign tasks to specific persons

[ziyi22]

Added functionality to assign tasks to specific persons in EffiTrack. Modified Task class to include a reference to the Person responsible for the task. Updated UniqueTaskList and AssignTaskCommand to handle the assignment of tasks to persons. Also added validation checks to ensure that a person can only have one task assigned at a time. Implemented necessary changes to ensure data consistency and integrity within the application.

[codecov]

Codecov Report

Attention: Patch coverage is 61.83575% with 79 lines in your changes are missing coverage. Please review.

Project coverage is 73.59%. Comparing base (40e43c3) to head (20bff25).

Files	Patch %	Lines
...eedu/address/logic/commands/AssignTaskCommand.java	26.92%	16 Missing and 3 partials ⚠️
.../java/seedu/address/model/task/UniqueTaskList.java	60.00%	8 Missing and 6 partials ⚠️
...c/main/java/seedu/address/model/task/Deadline.java	37.50%	10 Missing ⚠️
...in/java/seedu/address/storage/JsonAdaptedTask.java	62.96%	5 Missing and 5 partials ⚠️
src/main/java/seedu/address/model/task/Task.java	80.00%	2 Missing and 3 partials ⚠️
.../address/logic/parser/AssignTaskCommandParser.java	72.72%	1 Missing and 2 partials ⚠️
...ava/seedu/address/logic/parser/ParserTaskUtil.java	72.72%	3 Missing ⚠️
...rc/main/java/seedu/address/model/ModelManager.java	62.50%	3 Missing ⚠️
...u/address/storage/JsonSerializableAddressBook.java	70.00%	2 Missing and 1 partial ⚠️
src/main/java/seedu/address/logic/Messages.java	0.00%	2 Missing ⚠️
... and 5 more

Additional details and impacted files

@@             Coverage Diff              @@
##             master      #58      +/-   ##
============================================
- Coverage     75.54%   73.59%   -1.96%     
- Complexity      445      494      +49     
============================================
  Files            75       84       +9     
  Lines          1427     1632     +205     
  Branches        137      161      +24     
============================================
+ Hits           1078     1201     +123     
- Misses          314      373      +59     
- Partials         35       58      +23     

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[howen02]

LGTM

[yiwern5]

this line would throw an NullPointerException if the person do not have any task.

Suggested change

	tasks.remove(key.getTask());
	Task task = key.getTask();
	if (task != null) {
	tasks.remove(key.getTask());
	}