Update of py-interfacelift-downloader

I went ahead and updated the code... Great start, and I probably wouldn't have even considered doing this if you hadn't provided the code.  Kudos there!

I added:
- option parsing so users don't have to edit code
- run all downloads/http grabs from native code to avoid shelling out
- provide logging for easier debugging and daily cron summaries
- added exception handling where it seemed necessary

I don't check that the directory is 100% accurate, I just pull until the current image matches something that already exists on disk.  This will work for an initial pull that grabs everything, but there are some images I didn't like, so I can go in and manually delete those and not worry that the script will re-grab them at a later run time.  It also doesn't kill the interfacelift servers with extra requests.

Let me know what you think!

Thanks,
Elliott