File input area very large in Firefox

The file input area extended well beyond its confines in Firefox. This commit limits the clickable area to the widget in Firefox, and to the selector button in other browsers (which is good in IE because there is a security constraint in IE that makes it invalid to click on anything else to upload a file).

Compiling appears to have changed copyright notices and some file versions. I can resubmit this PR with just the change to fileinput.less if that's preferable?