Added ability to Edit to-do items in a list
Moved the becomeFirstResponder to the else clause

- We should only set focus to text box when adding new item
Txt field setting code moved to viewWillAppear

Since we want to display the text of the toDoItem object as the view
appears, the code needs to be in viewWillAppear.
Merge pull request #5 from akshay23/akshay/feature

Added ability to Edit to-do items in a list