Refactor DetermineDisplayMode method in Controller
Refactor ICommand to remove InvalidTaskNumberException
Add Constants.java in util package
Fix bug with next and back in UI, redirect user to the right page after command execution
Merging with Shotaro
Fix bug in UI for delete command execution
Merging with Andhieka
Merge pull request #145 from mikelimantara/master

Fix bug with next and back in UI, redirect user to the right page after command execution