General:
 * Use Nepomuk describeResource and storeResource to send somehow an additional
   trig or rdf file.
 * Investigate if channels are closed channels when transfer ends/fails
 * Save metadata about sender and receiver
 * Send multiple files in a tarball and extract them on the other side
 * Send single files compressed to save bandwidth and extract on the other side

Incoming file transfers
 * Close window if file transfer is cancelled
 * Ensure that when the file transfer fails or is cancelled the empty file is
   deleted and the .part file is left

Outgoing file transfers