Separate class for main function and controller

Public main function in LDo class and Controller in a new class.
Added try-catch block in exeuteCommand()
Merge branch 'master' into controller/sharon

Conflicts:
	sg/codengineers/ldo/controller/LDo.java
Cancelled try-catch block
Run shows welcome message and today's task list

When L'Do is run, it will show a welcome message and today's task list.
Edited exception handling in run()

Adjusted with changes in UI methods.
Added a try-catch block within the user interaction loop. Exceptions will
cause the system to print an error message, but not terminate. The system
will keep asking for the next user input.
Merge branch 'master' into parser/Victor

Conflicts:
	sg/codengineers/ldo/controller/LDo.java