[GUI] revert contact -> buddy wording

PART 10

Change-Id: Ie6ab502d7c5e4e6db25e35c7085048e3a1bd08a2
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/1197
Tested-by: Jenkins CI
Reviewed-by: Stefan Rossbach <srossbach@arcor.de>