exit function in Dwriter now checks for changes before exit
Added a UndoListener class
Added funtionality to SaveAction and SaveAsAction
Added funtionality to NewAction
Added funtionality to ExitAction
Added new function to Frame class and some changes

added getUndoManager() getTextArea() and getTextAreaScrollPane()
function.
Minor changes about the constructors of the actions.
deleted some unused variables.
added a UndoManager.
Added  the UndoListener created previously to the Document of the
textArea
Added functionality to some actions

RedoAction, SelectAllAction, TimeDateAction, UndoAction, WrapTextAction