[GUI] revert contact -> buddy wording

PART 8

Change-Id: I64f1893c4f1cd5d23b12676a1283e2000ae9ee4b
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/1194
Tested-by: Jenkins CI
Reviewed-by: Stefan Rossbach <srossbach@arcor.de>