plugin XEP-0047, XEP-0096: In-Band Bystream plugin cleaning: - some renaming, comments improvments, etc - progress callback is no more managed here, as it will be managed by application - no more file data is used, beside file_obj - a proper Deferred is used instead of success and error callbacks - more clean error sending method plugin XEP-0096 has been updated to handle changes. Its temporarily partially broken though