deform2: fix up file_upload.pt

This makes the FileUploadWidget look a bit nicer (and more legible).

More work is probably in order on this front.  I believe javscript is necessary to make the file upload control
match the other form controls.  A quick search has found two projects which might be useful, though neither
looks necessarily ideal:
- Jasny’s fork of  bootstrap 2.  Code [here](https://github.com/jasny/bootstrap/blob/master/js/bootstrap-fileupload.js), demo [here](http://jasny.github.io/bootstrap/javascript.html#fileupload).
- Also found this http://gregpike.net/demos/bootstrap-file-input/demo.html

Are there better choices?