SWC-1382

Added Drag & Drop functionality to file uploader.
It appears that every time the uploader is created, a new eventlistener for each event is added to the document (for each of these event types). Would this work if you targeted the actual element?  Like fileFieldElement.addEventListener("dragover", anonymousFunction, false)?  If not, another option is to init once, and have it reference a global (static) fileFieldId (I think we will only want to style a single drag and drop zone in the page)?