Delete unused import
implement getSubtask() and addSubtask(Task task) method
update the search method
Pass the unit test for createFile();
Pass the unit test for setFile(String);
Pass the unit test for addTask(Task) and deleteTask(Task);
Pass the unit test for updateTask(oriTask,newTask)
add clear before every unit test
update convetJSONToTask method
Pass the unit test for search(int [])
removed binary for merge
Merge remote-tracking branch 'origin/Storage'

Conflicts:
	CS2103T_ZombieTask_DatabaseAPI/.classpath
	CS2103T_ZombieTask_DatabaseAPI/bin/ZombieTask_StorageAPI/StorageAPI.class
	CS2103T_ZombieTask_DatabaseAPI/bin/ZombieTask_StorageAPI/Task.class
	CS2103T_ZombieTask_DatabaseAPI/src/ZombieTask_StorageAPI/StorageAPI.java
	CS2103T_ZombieTask_DatabaseAPI/src/ZombieTask_StorageAPI/Task.java
put in package to avoid same-name conflict with 'Command' class
removed json.sf files
Update implemented, unique exceptions added