Merge pull request #2 from mikelimantara/working

Added some tests and partially implement addCommand
Merge pull request #5 from mikelimantara/master

Add EditCommand, DeleteCommand, DisplayCommand minimally for parser to u...
Implemented IParser as Parser. Removed all references to JDK Calendar with own Date class.
Modify AddCommand for basic functionality of adding tasks
Add EditCommand fo basic functionality of editing a task
Add DeleteCommand for basic functionality of deleting a task
Add DisplayCommand
Modify ICommand and TaskManager for basic CRUD functionality
Add Controller class, without any method implementations
Fix conflicts in AddCommandTest and TaskManager while merging
Implement some of the methods in Controller