simplescan un-usable within script-based workflows.

Though the bug summary is a bit vague, specifically, I have in mind that simple-scan should provide commandline-options to control the following things:

- default save-to filename (so that it's possible to simply press the "Save" button without needing to set the location/filename via the GUI (to save to a different file, the "Save as" menu item can be used)
- scan resolution
- scan number-of-colors
- target filetype (though this should also be auto-detected if possible if a save-to filename is provided.

- (lower priority) "one-shot" mode which just makes a single-page scan and saves it without opening the GUI -- this might not be that necessary, but could be useful...

By making the first of these things available as commandline-options would make it possible to use simple-scan within shell scripts that specify particular target-file locations, and subsequently do postprocessing on the files. As it currently is, simple-scan is not suitable for being integrated into a script-based workflow, though I'd love to be able to use it in this way, since it provides a nice (and simple!) scanning interface.