Task storage load save

[Asuraxsoul]

Fixes #81
Add GUI related Task files, hide from GUI MainWindow for now.
Fixes #45
Save Task details into addressBook.txt data file in Json format.
Load Task from addressBook.txt data file still in progress.

[codecov-io]

Codecov Report

Merging #115 into master will decrease coverage by 3.93%.
The diff coverage is 9.34%.

@@             Coverage Diff              @@
##             master     #115      +/-   ##
============================================
- Coverage     62.68%   58.74%   -3.94%     
+ Complexity      507      498       -9     
============================================
  Files           102      105       +3     
  Lines          1865     1966     +101     
  Branches        177      189      +12     
============================================
- Hits           1169     1155      -14     
- Misses          648      760     +112     
- Partials         48       51       +3     

Impacted Files	Coverage Δ	Complexity Δ
.../java/seedu/address/logic/commands/AddCommand.java	28.57% <ø> (ø)	8.00 <0.00> (ø)
.../seedu/address/logic/parser/TaskCommandParser.java	0.00% <ø> (ø)	0.00 <0.00> (ø)
...c/main/java/seedu/address/model/task/Deadline.java	71.42% <0.00%> (-21.17%)	8.00 <0.00> (ø)
src/main/java/seedu/address/model/task/Event.java	77.14% <0.00%> (-22.86%)	9.00 <0.00> (ø)
src/main/java/seedu/address/model/task/Task.java	25.00% <0.00%> (-75.00%)	4.00 <0.00> (ø)
src/main/java/seedu/address/model/task/Todo.java	74.07% <0.00%> (-16.84%)	7.00 <0.00> (ø)
...in/java/seedu/address/storage/JsonAdaptedTask.java	0.00% <0.00%> (ø)	0.00 <0.00> (?)
src/main/java/seedu/address/ui/MainWindow.java	0.00% <ø> (ø)	0.00 <0.00> (ø)
src/main/java/seedu/address/ui/TaskCard.java	0.00% <0.00%> (ø)	0.00 <0.00> (?)
src/main/java/seedu/address/ui/TaskListPanel.java	0.00% <0.00%> (ø)	0.00 <0.00> (?)
... and 13 more

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[peironggg]

Nice job saving these Task info into .json, we rly need tht

[wilinetan]

Thanks for updating the GUI for tasks and saving tasks locally!