Rework networker
- keep netconfigs in hash; create the usual deserialize/delete/... functions
- keep the netmap in hash; create the usual de/serialize/delete/... functions
- change sequence: serialize & save netmap; combine spoolfiles; free netmap.
- use strbufs splice() wrappers to combine the message-spoolfiles into host-spoolfiles instead of forking a shell & running cat + rm
- when appending to host-spoolfile fails, remove partial adds to avoid creating invalid spool control files
- only cleanup spool directory if we successfully combined all files; else we might loose messages if i.e. a networker is running for that node.