BugFix - username filed was always disabled

• There was a problem with the enabled property of the Username object. The value of this property was set to true, when instance of this class was created. This property was used in the initWidget method. The initWidget method was called from a constructor of a super class and that was a problem. When the super constructor was called, variables declared in the Username class were not initalized. Therefore, the enabled property had the default value - false.
• This caused the username to be always disabled.
• I discovered that the property was not actually needed, so the fix is just to remove it.