Fixing destination filenames.

There used to be only 2 files in the webjar - `META-INF/resources/webjars/Eonasdan-bootstrap-datetimepicker/3.1.3/css` and `META-INF/resources/webjars/Eonasdan-bootstrap-datetimepicker/3.1.3/js`. This was hiding the non-minified file. Also, because the filenames didn't end with `.js` or `.css`, the contents were returned as `application/octet-stream` instead of `application/javascript`/`text/css`.