added file-output for plots

git-svn-id: https://gnunet.org/svn/gnunet@31047 140774ce-b5e7-0310-ab8b-a85725594a96
Fix issue 3154: gnunet_conversation_service.h doesn't get installed


git-svn-id: https://gnunet.org/svn/gnunet@31048 140774ce-b5e7-0310-ab8b-a85725594a96