Add URL support for MediaWiki images folder import

Currently, when selecting mediawiki+xml as a input source in Filter Streams, it says

Supported formats are file:<path in server> (e.g. file:/home/myuser/target.ext*) and *url:<url> (e.g. *url:http://myserver/some/file/to/parse.ext*). When empty it read the request input stream.

for the FILES input, it actually doesn't support url.