More os_slideshow basics.  #1331

- Forgot the link field.  Derp.  Added that in.
- Began working on the view.  I wasn't able to recycle the media gallery slideshow view, but most of the logic still works, including box options.
  - View needs to impose a size limit.  The image style has slideshow_$size formatters available, so I'm just going to mooch those and use the box option.
  - Was not expecting trouble here, but the link coming off the slideshow will need some attention.  Views rewrite rules (at least those present in the UI) weren't conditional.  I'm linking to field_link, even when it's empty.  Will probably have to go outside of views to get that right.
  - Couldn't find the views filter that lets you specify an array of values.  Could have sworn that existed.  Instead I made a separate filter group that's ORed together.  During $box->render() I add an item to that for each nid.  Works fine, but I'd like a cleaner option.
- slideshow_image nodes are not getting an og_group_ref.  Going to get basic functionality down before worrying about that.
- Still haven't updated the manual list sorting/preview.  That's next I think.