Switch to wxpython for the gui

* Create gui_main.py
* modify app.py to run the main loop
* modify the behavior of the renaming functions in directoryrenamer.py
    - It is now a class that includes a call back function. It no
      longer
    - performs checking on the input
Propogate errors up from subclasses

* modify filerename.py and imdbhelper.py to return useful error
  messages
Add setup.py for use with py2exe