Reimplement file stanza extension from XEP-0234: Jingle File Upload
Created by: LNJ2
The file stanza extension from Jingle File Upload is now also used for other protocols as XEP-0385: Stateless Inline Media Sharing (SIMS). Unfortunately, the original implementation was only usable in a full Jingle File Upload request. Thus, this new implementation was required. It would be preferable that this implementation is also used in the normal Jingle session, later.