TaskPanel now not part of Base, but of feature UI
Removed unnecessary this. in features Dates's Task
Added List import to class Shell
Task names are displayed centered in GUI now
TaskPanel displays Dates, if feature selected
Gui allows now addition of tasks with a date.

Added a static member FORMAT to each date-format feature to represent the expected format.
Removed unused variable in MainPanel
TaskInputPanel uses CLIReminder instead of Reminder interface now