[FEATURE] use MDNS to *connect* to the local area network

Added more MDNS stuff. Currently it is possible to connect to the local
area network and see other connected users.

Change-Id: I08e5e72aeb108d21fde64845f81f7a08a1a177c0
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/1601
Tested-by: Jenkins CI
Reviewed-by: Stefan Rossbach <srossbach@arcor.de>