Don't include partial image paths in templates

I sometimes try to make data entry easier by hard-coding partial paths in URLs and filenames. So, I started with "/img/small/" as part of the export templates, which made entering a small image as easy as pasting in the filename and letting the template figure out where it goes. This is nice and allows for easy global path changes. But, it limits flexibility. For example, I wanted to use the same $SmallImage attribute for my Movies template but the template prevented me from just pasting in a URL to Letterboxd copy of the cover art. So I changed it. Now, $SmallImage requires the full path or URL. Templates just link to whatever is in the attribute.