[INTERNAL] changed ITransferModeListener interface

Renamed to ITransferListener. The listener is now only being notified of
data transfers are now longer of connection changes.

Change-Id: Ia2928292e38a4a4f7fe3cd1de0319a028fd33764
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/1611
Tested-by: Jenkins CI
Reviewed-by: Stefan Rossbach <srossbach@arcor.de>