client manager: higher level client API with a transmission queue and message handler registration

git-svn-id: https://gnunet.org/svn/gnunet@33441 140774ce-b5e7-0310-ab8b-a85725594a96
PSYC util lib: receiving/transmitting/logging PSYC messages

git-svn-id: https://gnunet.org/svn/gnunet@33442 140774ce-b5e7-0310-ab8b-a85725594a96
psyc, multicast: reorg code, use new client manager & psyc util lib

git-svn-id: https://gnunet.org/svn/gnunet@33443 140774ce-b5e7-0310-ab8b-a85725594a96