Make TaskManager a singleton class
Finish converting list of tasks to JSONObject
Merge branch 'master' into storage

Conflicts:
	src/list/AddCommandTest.java
	src/list/Category.java
	src/list/Date.java
	src/list/DeleteCommandTest.java
	src/list/DisplayCommandTest.java
	src/list/EditCommandTest.java
	src/list/TaskManager.java
Finish converter for TASKS
Merge pull request #34 from mikelimantara/storage

Converter Class able to parse list of task to Json and vice versa