Decouple IOManager writes from GUIIO
Add an inner class to GUIIO that extends Writer and can be used  to
represent a file whose writes go to the GUIIO.
Decouple IOManager reads from GUIIO
Add an inner class to GUIIO that extends Reader and can be used to
represent a file whose reads are delegated to GUIIO.
Override correct method of the Writer abstract class