[GUI] revert contact -> buddy wording

PART 8

TODO: The messages should need a complete overhaul.

Change-Id: I0bd89ed7e677fef4df1c9e66665c8cfd49c29606
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/1195
Tested-by: Jenkins CI
Reviewed-by: Stefan Rossbach <srossbach@arcor.de>