Added attributes to the XML description for a module to specify preferred file types. Slicer uses this information to constrain the file browser to select files of the appropriate type. Slicer also uses this information to indicate the type of files a module can use for images. So if Slicer needs to write an image to disk to send to an executable command line module, the first file type listed will be the type of file used. The default is to use a nrrd file. If an executable command line module cannot understand nrrd, then they can specify another image format (meta, analyze, etc., whatever the Archetype writer can handle).