FileUploadByUrlDialog converted to UIBinder.
Expanded FileUploadByUrlDialog to have one status "spinner" per url box
for consistency with the SimpleFileUploadDialog. Also set up the start
of "feeding back" the server errors into the UI in the
FileUploadByUrlDialog. The errors are currently going into the
individual fields, and are not summarized on the window as a whole.
Need to test the "blink" fx on error as well.