Update the whole file item instead of only its contents

The "done" and "fail" callbacks both update the item for the uploaded
file using "setFileIcon". "setFileIcon" updates the contents of the
"<li>" element for the file, but the "fail" callback was giving
"setFileIcon" an element generated by the template,  so the resulting
HTML contained a "<li>" element nested in another "<li>" element.

However, generating the HTML is better done through a template, so the
template now receives the icon to show in order to be used by a
successful upload and a failed one, and "setFileIcon" was changed to
"updateFileItem".

Note that the mimeTypeUrl does no longer need to be escaped, as
Handlebars templates escape the needed characters automatically.

Signed-off-by: Daniel Calviño Sánchez <danxuliu@gmail.com>