[GUI] revert contact -> buddy wording

PART 1

Change-Id: Icf702d725b4fec7e1f09d552b4ed1de6258f63f5
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/1186
Tested-by: Jenkins CI
Reviewed-by: Stefan Rossbach <srossbach@arcor.de>