Image Quality enhancements

I noticed that the scaling wasn't quite as nice as it could be. A quick Google search led me to this article: http://www.olsonsoft.com/blogs/stefanolson/post/Workaround-for-low-quality-bitmap-resizing-in-WPF-4.aspx

I implemented those changes and now the generated images/previews look much better. 

I also made it so that when an image is opened, the whole thing is used automatically as the preview image... I was having trouble trying to click in the corners to select the whole thing, so this just does it from the get-go.