Slider does not honour selected image size when choosing the background image

[PeterUpfold]

Since the change to storing the image attachment ID instead of URL, if you pick a very large image for the background URL, but choose one of the smaller sizes (medium, large), this works initially in the editor, but when saved, the full-size image is used.

Total Slider should store the desired image size and use that as well as the attachment ID to determine which image URL to show at display-time.

[chrisvanpatten]

I think there's a lot of work to do w/r/t image sizes and positioning/cropping, which should be (in my estimation) a goal of TS 1.2, particularly as the new media uploader matures and we look to integrate with that.