WIP: First step for file transfers in log window
Defined new messages types for log (FILE_RECV, FILE_SENT) and added functions to logger.py to add these into the log. These function are called in jingle_session. For now only for the functions that get called when receiving a file. It doesn't work right now, because session_terminate is called from a different thread and it is only ok to modify the database from the mainthread.