1. Present a helpful GUI error message if the call to xmlNew returns Nothing.

2. Modify the podcatcher to be able to run with either the GUI or the
   command-line interface from a single code base. Hint: move common code out of
   PodMainGUI.hs, then have two different Main modules, one for the GUI, and one
   for the command line.




Testing 1.:
  Steps:
    - Compile PodMainGUI
    - Remove podresources.glade file
    - Run PodMainGUI
  Result:
    - Error dialog window informing that podresources.glade file has not been
      found is displayed


Testing 2.:
  Steps:
    - Compile PodMainGUI
    - Run PodMainGUI
    - Add a podcast
    - Click Update
    - Click Download
  Result:
    - The mp3 files have been downloaded

  Steps:
    - Exit PodMainGUI
    - Remove pod.db file
    - Remove the mp3 files
    - Run PodMainGUI
    - Add a podcast
    - Click Fetch
  Result:
    - The mp3 files have been downloaded

  Steps:
    - Exit PodMainGUI
    - Compile PodMainCLI
    - Run PodMainCLI
    - Add a podcast
    - Run Update
    - Run Download
  Result:
    - The mp3 files have been downloaded

  Steps:
    - Exit PodMainCLI
    - Remove pod.db file
    - Remove the mp3 files
    - Run PodMainCLI
    - Add a podcast
    - Run Fetch
  Result:
    - The mp3 files have been downloaded