Added the implementation for the button at the RootWindowContoller. Need to make method that change the view to the home screen
Merge pull request #138 from liafailboy/working

Added the implementation for the button at the RootWindowContoller. Need...
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
Merge pull request #146 from andhieka/working

Category Commands
Fix bug in UI for delete command execution
Merge with michael
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
Removed the viewing modes from category hashmap
Set window key press handler