sart an due date

* add option for start and due date
* colored output (style.css)
* show the innertext of a todoitem as a link to the page where the todo is located
* for the option 'header' add the value 'none' to hide the header in list views

- still missing is functionality to filter todos by start/due date in list views

i changed parameters of function createTodoItem so we have less parameters, be a more flexible to implement new options